Part Type
Custom Shaft Couplings and Couplers
A custom shaft coupling is quoted here when no catalog coupling has the bore pair, keyway or length your drive needs. Rigid clamp, set-screw and keyed couplings are turned to your print from one piece up, and the metal hubs of a jaw or Oldham coupling are made to it as well. Send the print or a STEP file through the quote form and a person quotes it in 24-48 hours.
Updated September 2026
Example part, modeled for illustration.
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Two bores, a keyway, and a length the catalog never has
Which coupling styles can be made to a print?
A coupling joins two shafts at their ends so one can transmit power to the other (source 1). The styles in the table are rigid couplings: they do not compensate for misalignment, so they belong on shafts that are already in line (source 1). Motion Control Tips puts the parallel misalignment most engineers accept for a rigid coupling at well below a thousandth of an inch (source 2).
A threaded coupler that joins two rod ends or studs is quoted as a custom fastener, and a threaded pipe coupling or reducer as a custom fitting. A flanged coupling is a short sleeve with a perpendicular flange (source 1); its bolt pattern goes on the print the way custom flanges describes.
Flexible styles do a different job, and only their metal hubs are quoted here. A jaw coupling is two hubs with a spider between them, usually elastomer, and an Oldham coupling is two hubs and a torque-transmitting center disc joined to each hub by tongue and groove (sources 1 and 2). The hubs are made to your print; the spider or center is the part you buy, as the question on hubs below explains.
| Style | How it holds the shafts | Put on the print |
|---|---|---|
| Set-screw | Screws bear on the shaft and can leave dents that make the coupling hard to adjust or remove (source 3). Machine Design suggests set-screw couplings only for low loads with no shock loading (source 4). | Screw size and position, and whether the shaft has a flat |
| One-piece clamp | A body bored to fit snugly over close-tolerance shafting, closed by clamp screws (source 3), with no machining into the shaft (source 4) | Bore size and fit, slot, screw size |
| Two-piece clamp | Split along its axis, so it assembles around both shafts without moving either one (source 3) | Bore size and fit, screw size and count |
| Keyed | A key carries the torque, and the phase between the two shafts is fixed (source 3) | Keyway width and depth |
What do the callouts on a coupling print mean?
A coupling print is short, and each line answers something the quote cannot guess. The table reads the callouts in the order a buyer usually writes them; the sections below go further on fits, keyways and alignment.
| Callout | What it means | What the print must show |
|---|---|---|
| Bore | The hole each end takes a shaft in; the two ends can be different sizes (source 3). | Size and tolerance, or an ISO fit class, for each end (source 5), in inch or metric |
| Keyway | A slot in the bore that takes a key, which fixes the angular relationship between the two shafts (source 3). The key width follows the shaft diameter (source 15). | Width, depth and tolerances, and whether it runs the full length of the bore (source 7) |
| Set screw | A radial screw that bears on the shaft or over the key. It can dent the shaft or keyway (source 3); a flat on the shaft where it seats reduces the chance of slipping (source 16). | Thread size, how many, their angle from the keyway, and whether the shaft has a flat |
| Hub OD | The outside diameter of the hub or body. | The diameter of each hub and any step between them, against the space the coupling runs in |
| Length | How far the coupling spans between the two shafts. | Overall length, the depth of each bore, and the gap left between the shaft ends |
| Material | The grade the coupling is turned from. | The grade, named (see the material section below) |
What should the print say about each bore?
Give each end its own size and fit; the two shafts may need different ones. A fit can be written as a size and tolerance or as an ISO fit class. In the hole-basis system, H7/g6 is a sliding fit that assembles easily and turns freely, H7/h6 a location fit that assembles without force, H7/k6 a transition fit that goes together with a rubber mallet, and H7/p6 a light press fit assembled by cold pressing; hubs are among the examples given for the last two (source 5).
Key width follows shaft size. The inch standard is ASME B17.1 (ANSI B17.1) and the metric one is DIN 6885 (sources 14 and 19). The table below is a published reference for the inch series, not a quote and not the standard itself; for metric, a published DIN 6885 chart puts a 22-30 mm shaft on an 8 mm key (source 6). Put the keyway width and depth on the print with their tolerances, and say whether the keyway runs the full length of the bore: broaching is mainly used for square-cornered internal keyways, and one that stops short of the end is largely cut by shaping or slotting instead (source 7).
For a D-shaped shaft, give the bore’s dimension across its flat. A splined bore is quoted too; put its full spline callout on the print. The flat, keyseat or spline on the shaft itself goes on the shaft’s own print, and custom shafts and pins covers that side of the joint. Keyways, flats, splines, clamp slots and screw holes are quoted from the print with the turned body.
| Shaft diameter, over and up to (in) | Key width (in) |
|---|---|
| 5/16 to 7/16 | 3/32 |
| 7/16 to 9/16 | 1/8 |
| 9/16 to 7/8 | 3/16 |
| 7/8 to 1-1/4 | 1/4 |
| 1-1/4 to 1-3/8 | 5/16 |
| 1-3/8 to 1-3/4 | 3/8 |
| 1-3/4 to 2-1/4 | 1/2 |
How are the two bores kept in line?
Tie one bore to the other on the print with a runout or position callout. Concentricity was removed from ASME Y14.5 in the 2018 edition, and GD&T Basics recommends runout or position in its place because they are much easier to measure (source 8). Position, perpendicularity and runout callouts are quoted from the print.
A bore that needs a ground finish, or a tighter fit than turning holds, is quoted with precision grinding as one job. Rush 1-2 weeks applies to machined parts with no secondary operations. Heat treat, grinding, EDM and finishing add time, and the quote gives the real date. Lead time starts at order approval. Put your need date in the part description and the quote answers it.
Which material should a shaft coupling be?
6061 aluminum is about a third the density of steel (source 9), so the same coupling in aluminum weighs about a third as much and carries about a third of the rotating inertia. Steel is stiffer: its Young’s modulus is about 200 GPa against 68 GPa for aluminum (source 10), so a steel coupling of the same size flexes less under the same load. Stainless steel carries at least 10.5% chromium, which forms a passive film against rust and corrosion (source 11). For stainless, name 303 or 304, or 316, whose molybdenum gives it more resistance to chlorides than 304 (source 12). Other alloys and plastics quoted on request. Name the grade on the print.
A finish called out on the print is quoted with the part. Anodizing grows into and out of the surface by equal amounts, so each surface gains half the oxide thickness (source 13) and a bore closes by about the full coating thickness. Say on the print whether the bore is masked during anodizing or sized for the coating; a common drawing note is that dimensions apply after all surface finishes (source 13).
How do I order a custom shaft coupling to a print?
Start from the two shafts, not the coupling. Measure each shaft’s diameter, any flat or keyway on it, and how far it reaches into the coupling, then write the callouts from the table above on one print. A fully dimensioned 2D PDF is quoted without a CAD line, and a STEP file with a PDF is the ideal package. A STEP file with no drawing is quoted to a ±0.005 in general tolerance, or the one your notes name, so write the bore fits and the keyway in the notes. A dimensioned sketch or a new sample part can also start a quote, and CAD from a sketch or sample is quoted as its own line; photos start the conversation, as the question on remaking a coupling explains.
Ask for more than one quantity, such as 1, 25 and 100, and the quote shows each. A production quantity can also be quoted in full and delivered in releases as a blanket order. Price, release schedule and lead time per release are set in the quote. Other parts for the same drive, such as bushings or anything else on the machined parts index, can go on the same quote.
Card by secure link (a processing fee applies), ACH, wire or check. Shipping is quoted as its own line, or ships on your carrier account. If a part doesn’t match the print, it’s remade or credited.
Sources
All accessed 30 September 2026. Where a figure here differs from your print, the print governs.
1. Wikipedia, "Coupling": en.wikipedia.org/wiki/Coupling (connects two shafts at their ends to transmit power; rigid couplings cannot compensate for misalignment; flanged rigid couplings are short sleeves with a perpendicular flange).
2. Motion Control Tips, "Couplings for PT and motion designs: Technical Summary", updated May 2015 by Mike Santora: motioncontroltips.com (rigid couplings need parallel misalignment well below a thousandth of an inch and cannot be run at high speeds; jaw coupling hubs and spider; Oldham hubs and center).
3. Arthur Stafford, "The Rigid Link", Machine Design, 1 November 2010: machinedesign.com (set screws dent the shaft; clamp coupling bored to fit close-tolerance shafting; two-piece couplings assemble without moving the shafts; keyways fix the phase; stepped bores join metric and inch shafts).
4. Jeff Kerns, "What’s the Difference Between Rigid-Coupling Types?", Machine Design, 7 December 2015: machinedesign.com (set-screw couplings for low loads with no shock loading; clamp couplings need no machining into the hub or shaft; keys wear over time and can develop backlash).
5. Wikipedia, "Engineering fit": en.wikipedia.org/wiki/Engineering_fit (ISO hole-basis fits H7/g6, H7/h6, H7/k6 and H7/p6, with hubs among the examples for k6 and p6).
6. National Machine Tool Co., "Key & Keyway Size Chart: Standard Dimensions (ANSI B17.1 & Metric)", 1 July 2026: keyseaters.com/local/keyway-dimensions-size-chart-ansi-b17-1-metric-reference-national-machine-tool/ (DIN 6885 metric rows: 8 mm key for 22-30 mm shafts; 2 mm key for 6-8 mm shafts).
7. Wikipedia, "Key (engineering)": en.wikipedia.org/wiki/Key_(engineering) (broaching for internal keyways; shaping or slotting for keyways that do not run the full length; set screws often accompany parallel keys to lock the mating parts).
8. GD&T Basics, "Concentricity": gdandtbasics.com/concentricity/ (concentricity removed from ASME Y14.5-2018; runout or position recommended in its place).
9. Wikipedia, "Aluminium": en.wikipedia.org/wiki/Aluminium (density about one-third that of steel).
10. Wikipedia, "Young’s modulus": en.wikipedia.org/wiki/Young%27s_modulus (aluminium 68 GPa; A36 steel 200 GPa).
11. Wikipedia, "Stainless steel": en.wikipedia.org/wiki/Stainless_steel (10.5% or more chromium forms a passive film against rust and corrosion).
12. Wikipedia, "SAE 316L stainless steel": en.wikipedia.org/wiki/SAE_316L_stainless_steel (molybdenum gives greater resistance than 304 to localized attack by chlorides).
13. Wikipedia, "Anodizing": en.wikipedia.org/wiki/Anodizing (oxide grows into and out of the surface by equal amounts; each surface grows by half the oxide thickness; "dimensions apply after all surface finishes").
14. Design World, "How do you specify keyways?", 9 May 2016: designworldonline.com (keyway dimensions are in Machinery's Handbook, ANSI B17.1 for inch and DIN 6885 for metric; a quoted coupling supplier’s product manager says keyways can wear out under load changes, reversals or indexing, that keyless clamping hubs have no relative movement between shaft and hub, and that holding torque depends on proper shaft and bore fit tolerances and on assembly screw torque).
15. Engineers Edge, "Shaft Diameter vs Key Sizes" (ANSI B17.1 table), undated, page copyright 2000-2026: engineersedge.com (key widths by shaft diameter range, 3/32 in for 5/16 to 7/16 in through 1/2 in for 1-3/4 to 2-1/4 in, tabulated above).
16. Wikipedia, "Set screw": en.wikipedia.org/wiki/Set_screw (a flat machined on the shaft where the screw contacts it reduces the chance of slipping and increases load capacity; keys and keyways are used instead of, or together with, set screws where high torque is needed).
17. Pepperl+Fuchs, "Sensors and Systems, North American Catalog", page 738, undated: files.pepperl-fuchs.com/online-catalogs/911360/files/assets/basic-html/page738.html (a rigidly mounted rotary encoder makes an over-determined system; a flexible coupling must be used between the encoder and the drive shaft to prevent high bearing loads).
18. AMES Web, "Set Screws Over Keys", undated: amesweb.info (diameter selections for set screws used over keys are given in ANSI B17.1).
19. ASME, "B17.1-1967 (S2023) Keys and Keyseats": asme.org (the standard's own listing; size, type and tolerances of parallel and taper keys and keyseats; the standard itself is not reproduced here).
Questions
Before you send a job.
01 What size keyway goes with a 1/2 inch bore?
A published ANSI B17.1 table puts a shaft over 7/16 in and up to 9/16 in on a 1/8 in key, so a 1/2 in bore takes a 1/8 in keyway width (source 15). That is a reference, not a quote: where a shaft sits on a range limit, check the standard, and put the keyway width, depth and tolerances on the print so the coupling is quoted from it. For metric, a published DIN 6885 chart puts a 6-8 mm shaft on a 2 mm key (source 6).
02 Can one coupling take an inch shaft on one end and a metric shaft on the other?
Yes. A stepped bore joins shafts of different diameters, and Machine Design’s article on rigid couplings names metric and inch combinations among them (source 3). The two ends are quoted as one part.
03 Should a coupling on a motor that reverses be keyed or clamp-style?
Both are quoted to your print, and the quote carries no torque rating. Two trade-press pieces bear on the choice: Machine Design notes that keys wear over time and can develop backlash (source 4), and a Design World article quotes a coupling supplier’s product manager who says a keyway connection can wear out under load changes, reversals or indexing, and that a keyless clamping hub has no relative movement between shaft and hub, with a holding torque that depends on proper shaft and bore fit tolerances and the right screw torque (source 14). Whichever you pick, put the fit for each bore on the print.
04 Where does the set screw go relative to the keyway?
The print should say, because the screw holes are quoted as drawn. The trade-offs are published: set screws can dent the shaft or keyway (source 3), a flat on the shaft where the screw seats reduces the chance of slipping (source 16), set screws often accompany a key (source 7), and ANSI B17.1 carries diameters for screws used over keys (source 18). Give the thread size, the number of screws, their angle from the keyway, and whether the shaft has a flat.
05 What torque or speed will a custom shaft coupling handle?
The quote carries no torque or speed rating. Size the coupling from your own load and speed, and put the operating speed in the part description. Motion Control Tips notes that rigid couplings are susceptible to vibration and cannot be run at high speeds (source 2).
06 Do you make the whole flexible coupling, or only the hubs?
The metal hubs. They are made to your print, jaws or slot included, and a hub made to mate a named catalog spider or center can be quoted from that coupling maker’s published dimensions. The spider or center disc is not included; you buy it.
07 Can a rigid coupling join a motor shaft to an encoder shaft?
Check with the encoder maker first. One encoder catalog says a rigidly mounted rotary encoder makes an over-determined system and that a flexible coupling must be used between the encoder and the drive shaft to prevent high bearing loads (source 17). A rigid coupling belongs on shafts that are already in line (source 1). If the joint needs a flexible element, the hubs of a jaw or Oldham coupling can be quoted to mate the catalog spider or center you name. Send both shaft diameters with tolerances, any flat or keyway on each, the gap between the shaft ends, and the largest outside diameter the coupling can have.
08 Can you remake a coupling with no drawing?
If it is a catalog coupling still sold under its maker’s part number, order it by that number from a distributor. A coupling nobody stocks any more, or one made to a print that is now lost, can be remade from a new sample part. The sample ships back with the parts. Start with photos and a note on where it fits; the reply says what to ship, and measuring the part and building the new model and print are quoted as their own line, the way reverse engineering describes. The new coupling is then quoted from the new print.
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