Fixtures
Custom Masking Fixtures and Racks, Machined to Print
A reusable machined shield that keeps the faces and bores that must stay bare out of the coating, batch after batch.
A masking fixture is a machined tool that covers or plugs the features of a part that have to stay bare while the rest is coated, and holds the part through the line. It replaces hand-applied tape and plugs on a part that runs often enough for the labour to matter. Materials follow the process temperature and chemistry. Send the part print with the masked features marked and the process named; a person quotes in 24-48 hours, standard lead time 4-6 weeks.
Updated September 2026
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Commercial work only. We don’t quote firearms, DoD, ITAR, or EAR-controlled parts.
What a masking fixture is, and who it is for
Selective finishing is ordinary: a bore that has to stay at size after anodize, a ground face that must not carry powder, a tapped hole that a coating would change the fit of, a ground strap location that has to stay conductive. On small quantities, tape, caps and plugs do the job by hand. On a part that runs monthly, hand masking is the slow and inconsistent step, and a machined fixture that plugs, shields and holds in one motion is what replaces it.
Two things are worth saying plainly. Finishing itself is outsourced here: the finish is specified on the print and quoted with the part, and parts come back finished and inspected. What is quoted on this page is the machined masking tool, made to your print, for you or your finisher to use on the line. Buyers sending the tool to their own plater or coater are the common case, and that is exactly how it is quoted.
Plugs, shields and hold-downs: the three jobs in one tool
A masking fixture usually does three things at once. It plugs: a machined pin or boss enters a bore or a tapped hole, sized so coating cannot creep past but the part still comes off after. It shields: a plate or a cap covers a face, held against it so the edge of the coating lands where the print says. And it holds: the part is retained through dipping, draining, spraying or an oven cycle without a hand on it.
Which of the three dominates changes the design. A wet process wants drainage and no traps that carry solution to the next tank. A powder line wants a hold that leaves a small, hidden contact point and survives the cure oven. A part with one critical bore may only need a plug and a hanger; a part with six masked faces needs a fixture built around it. Describe the process on the print and the tool follows it.
The masking edge, and the tolerance question nobody asks
The most common disappointment with a masking tool is the edge: coating that creeps under a shield, or a bare band wider than the print allows. That edge is a contact question. Where the shield meets the part, the fixture has to bear on a real surface with real pressure, and if the part varies at that surface the shield floats and the coating walks under it. So the print should say where the masking boundary is and how much it may move, in a number.
A bore plug has the same issue from the other side: too loose and coating gets in, too tight and the plug seizes as the part expands in the oven or the tank. That is why the plug diameter on the print should be a clearance from the finished bore size, stated, and not "a nice fit". Thermal growth over a cure cycle is the usual reason a plug that worked cold sticks hot, and it is worth calling out on the print if the process runs warm.
Materials: what survives the bath and the oven
Anodizing runs in acid at moderate temperature; powder coat is cured in an oven, and Wikipedia’s Powder coating entry (en.wikipedia.org/wiki/Powder_coating) describes the powder being heated until it flows and cures, commonly in the 350 to 400°F region, which rules out most ordinary plastics on contact faces. Aluminum tooling and shields are common for powder work because they take the heat and machine cleanly, and titanium is the classic rack and fixture material on the anodize side because it does not anodize significantly itself and survives the chemistry. Titanium and 6061 are both quoted from print.
Where a soft, non-marking contact is needed and the temperature allows it, Delrin and UHMW are the usual choices, with acetal holding size well (en.wikipedia.org/wiki/Polyoxymethylene) and UHMW being softer and more slippery (en.wikipedia.org/wiki/Ultra-high-molecular-weight_polyethylene). Neither belongs on a powder cure face. Silicone caps and plugs are catalog items with published temperature ratings and sizes (mcmaster.com/products/masking-plugs/), and they go on the print by part number where the tool holds them rather than replacing them.
What to send, and what the quote will ask
Send the part model and a PDF print with the masked features marked and the masking boundary dimensioned with its allowed movement, the process and its temperature and chemistry, whether the tool also has to hang or carry the part, the batch size per load, whether the tool is reused indefinitely or is consumable, and any catalog caps or plugs you want it to carry. Any file type is accepted; STEP plus PDF is ideal.
The quote will ask about the things that decide whether a masking tool works: how much the part varies where the shield contacts it, what the process temperature is, and whether solution has to drain. Anything on the print that cannot be made or inspected as drawn is named rather than substituted. Finish callouts on the parts themselves are covered on CNC surface finishes.
Inspection, quantity and lead time
Every fixture is inspected against its print before it ships. What paperwork ships with a fixture is covered on check and inspection fixtures.
One tool or a rack of them is a normal order, and there is no minimum; a set sized to a full load is quoted as one order. 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. Standard lead time is 4-6 weeks, and extended is 6-8 weeks when timing is flexible; the quote comes back in 24-48 hours. Lead time starts at order approval. Put your need date in the part description and the quote answers it. Vendor setup takes a day: W-9, NDA, net terms available.
Questions
Before you send a job.
01 Do you do the anodizing or powder coating as well?
Finishing is specified on the print and quoted with the part, and parts come back finished and inspected. What this page quotes is the machined masking tool itself, made to your print, for you or your finisher to run. Many buyers order the tool here and send it to the plater or coater they already use.
02 What material should a masking fixture be?
It follows the process. Titanium is the classic anodize rack and fixture material because it does not anodize significantly and survives the chemistry; aluminum suits powder work, where the cure oven commonly runs in the 350 to 400°F region. Delrin and UHMW give soft, non-marking contact where the temperature allows, and do not belong on a powder cure face.
03 Why does coating creep under my mask?
Almost always because the shield is not bearing on the part with real pressure at the boundary, usually because the part varies at the contact surface and the shield floats. Dimension the masking boundary on the print and state how far it may move, and say how much the part varies there, so the contact is designed rather than hoped for.
04 How tight should a bore plug be?
Tight enough that coating cannot creep past, loose enough that the part releases after the process. Call it out on the print as a stated clearance from the finished bore size rather than as a fit by feel. If the process runs warm, say so: thermal growth over a cure cycle is the usual reason a plug that worked cold seizes hot.
05 Can you make a full rack for a whole load?
Yes, and a set sized to a full load is quoted as one order. Give the batch size per load, the hanging or carrying arrangement, and the drainage requirement if it is a wet process. There is no minimum, so a single tool is equally normal.
06 What should I send to get a masking fixture quoted?
The part model and print with the masked features marked and the boundary dimensioned, the process with its temperature and chemistry, whether the tool hangs or carries the part, the batch size, and any catalog caps or plugs it should hold. Any file type is accepted and the quote lists what is missing.
Related
Where to go next.
Custom machined fixtures
The hub: every fixture family, quoted from your print.
View →CNC surface finishes
How a finish is called out and quoted with the part.
View →Aluminum tooling plate fixtures
MIC-6 and ATP-5 bases, and what they hold flat to.
View →Get a quote
Any file type; STEP + PDF ideal. A person replies in 24-48 hours.
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