Custom Machined Knobs

The knobs that get turned to print

Most knobs come down to a handful of jobs. Control and pointer knobs sit on a potentiometer, switch, or encoder shaft and show where the setting is. Clamping and fixture knobs carry a threaded stud or a tapped hole so an operator can lock a jig or a guard by hand. Star, lobe, and wing knobs give fingers something to grab. Knurled adjustment knobs and thumb wheels handle fine settings, and hand wheels and crank knobs drive a leadscrew or a valve. Instrument and equipment knobs round it out wherever a panel needs a grip that matches.

What they share is that the catalog version is often close but not exact: the thread is metric when you need imperial, the bore does not match your shaft, the knurl is wrong, or the look does not suit the rest of the build. Those get turned from bar to the right diameter and profile, then milled for flats, lobes, or a pointer where the grip calls for it. One replacement knob for a machine, or a matched set for a panel, both quote the same way.

Grip: knurl, flats, lobes, and pointers

The grip is the whole point of a knob, so it is worth calling out clearly. Knurling puts a pattern into the rim so hands get a better hold than on a smooth surface, and control knobs on electronic equipment are frequently knurled (source 1). The diamond pattern is the most common type on everyday objects, and straight knurling is grooves parallel to the axis (source 1). ASME B94.6 covers the knurling tools and blank dimensions for straight, diagonal and diamond knurling on cylindrical surfaces (source 2). Milled flats, scalloped lobes, and star or wing shapes are the other grips a print can call out, and a thumbscrew head, with ridged or knurled sides, is the familiar part made to be tightened and loosened by hand (source 3). A knurl is called out by type, pitch and axial length (source 4), so name those, or the lobe count and profile, and the grip comes out the way you picture it.

A pointer or an index flat turns a knob into a control you can read, and a pointer used with a scale helps produce repeatable settings (source 5). Common forms are a raised arrow, a skirt with a flat for a set mark, or a D-shaped profile that lines up with a scale. If the knob shows a position, say where the pointer sits relative to the bore or the flat and it gets cut to match. Call out a chamfer or radius on cosmetic edges so nothing is sharp in the hand.

Threads, bores, and how it mounts

How the knob mounts is the other half of the print. A tapped female thread (through or blind) screws onto a stud or a leadscrew; a male stud turned onto the back bolts the knob into a jig; a plain bore with a set screw clamps onto a shaft; and a D-bore or a flatted bore matches a flatted shaft. Give the thread size, pitch, and class (for example 1/4-20 UNC 2B or M6x1.0), or the shaft diameter and the fit you want, and note whether a tapped hole is through or blind with its usable depth.

A knob with a turned male stud sits next to custom fasteners, which are quoted to the print the same way. For a set-screw knob, the screw’s point matters: the cup point is the most common type, and a flat milled or ground on the shaft where the point lands reduces the chance of slipping and increases load capacity (source 6). Say which you want on the print. On a plastic knob, a threaded insert, typically brass or stainless, is one way to put a metal thread in the plastic (source 9). If a knob needs a threaded insert, put it on the print; the insert is supplied and installed to the print.

Materials and finishes

6061 aluminum is a common starting point, and anodized aluminum can be dyed in many colors (source 10). That lets a knob be keyed by color so a row of identical knobs reads red, blue, and black on a panel instead of getting mixed up; anodic color is used to tell medical devices, components and controls apart (source 10). Brass has a bright, golden look and is used for drawer pulls and doorknobs (source 11), which makes it a pick for a decorative or instrument knob. Stainless resists rust through its chromium content and is used where cleanability matters, as in food processing plants (source 12); for chloride and marine duty see 316, where molybdenum improves resistance to pitting corrosion (source 12). Steel suits a hand wheel that should have some weight, and Delrin or acetal is a free-cutting plastic and an electrical insulator, and the plastic is used for parts that need low friction (source 13). Other alloys and plastics quoted on request. Name the grade on the print.

Finishes follow the look you want. Anodize in clear, black, or color adds wear and corrosion resistance (source 10). Passivation applies to stainless, and a Delrin knob is left as-machined. A finish called out on the print is quoted with the part. Every part inspected against your print before it ships. Knobs usually accompany a panel or a fixture, and both are on the parts index. A billet bezel that frames the panel the knob sits on is quoted the same way.

Sources

All accessed 4 October 2026. Where a figure here differs from your print, the print governs.

1. Wikipedia, "Knurling": en.wikipedia.org/wiki/Knurling (diamond and straight patterns; grip; control knobs frequently knurled).

2. ASME, "B94.6-1984 (S2025), Knurling": asme.org (scope: knurling tools and blank dimensions for straight, diagonal and diamond knurling on cylindrical surfaces).

3. Wikipedia, "Thumbscrew": en.wikipedia.org/wiki/Thumbscrew (ridged or knurled sides; tightened and loosened by hand).

4. Engineers Edge, "Dimensioning Knurled Features Drawings": engineersedge.com (knurl types; a knurl called out by type, pitch and axial length).

5. Wikipedia, "Control knob": en.wikipedia.org/wiki/Control_knob (a pointer used with a scale helps produce repeatable settings).

6. Wikipedia, "Set screw": en.wikipedia.org/wiki/Set_screw (cup point most common; a flat on the shaft at the point reduces slipping and increases load capacity; potentiometer knob example).

7. Wikipedia, "Unified Thread Standard": en.wikipedia.org/wiki/Unified_Thread_Standard (thread designation; classes 1B, 2B and 3B for internal threads; UNC coarse).

8. Wikipedia, "ISO metric screw thread": en.wikipedia.org/wiki/ISO_metric_screw_thread (M designation; M6 coarse pitch 1.0 mm).

9. Wikipedia, "Threaded insert": en.wikipedia.org/wiki/Threaded_insert (inserts give plastic parts a metal thread, typically brass or stainless).

10. Wikipedia, "Anodizing": en.wikipedia.org/wiki/Anodizing (wear and corrosion resistance; porous film accepts dyes; color used to distinguish medical devices, components or controls).

11. Wikipedia, "Brass": en.wikipedia.org/wiki/Brass (bright, golden appearance; drawer pulls and doorknobs).

12. Wikipedia, "Stainless steel": en.wikipedia.org/wiki/Stainless_steel (chromium passive film; cleanability in food processing plants; molybdenum and pitting resistance).

13. Wikipedia, "Polyoxymethylene": en.wikipedia.org/wiki/Polyoxymethylene (sold as Delrin; free-cutting; electrical insulator; applications needing low friction).