Match Masking Caps to Common Threaded Studs

The correct caps for SAE/UNC/metric threads - see chart below

A typical call out on engineering drawing is to mask threaded pins or other threaded features. This protects them from powder coating, paint, anodizing, plating, ecoating and other metal finishing processes so the threads stay clean for when a nut is added later. But masking those studs presents a challenge:

How do you determine the right cap to use on a given thread? 

Viadon can help with the chart below showing common threads in SAE, UNC and metric size with the correct masking caps in the associated row. Scroll down for the chart; for a bit more detail about each type of cap, read on. 

Standard and Expandable Silicone Caps for Threaded Studs

For a standard cap that just needs to be covered for most coating types, a straight wall cap is used like Viadon's SC line of silicone caps. With a wide range of caps available, some in various lengths for the same inside diameter of the cap, in every case there is a cap to cover every common SAE / UNC / metric thread size and type. Click on the first link below for more options. 

When fewer caps are desired, our line of SCE expandable caps may be used instead - some of these caps can be used on multiple thread sizes. Click on the second link below to see more. 

• SC line of straight wall caps for common thread sizes 
• SCE line of expandable caps

Silicone Caps with a Flange for Grounding Areas

There are times when a threaded stud needs an uncoated area to provide for an electrical ground. When masking these features, a fast and easy way to accomplish this is with a flange cap. Viadon's VFC line of caps with a grounding flange are perfect for these types of situations, and a wide range of options are available fornearly every common SAE / UNC / metric thread size.  Click on the link below for all flanged caps. 

• VFC line of flange caps for grounding areas

Download the chart below in PDF format for printing / quick reference

Don't see the thread listed below for which you need a cap? Email us at [email protected] or give us a call at 866-534-3900 - we actually pick up our phone during business hours - for real! (7:30 am to 4 pm Central Time)

Common threads & caps for thread sizes

Thread size	Caps for thread sizes
	Straight‑wall caps	Expandable cap	Cap with flange
4‑40	SC100‑0500 & SC100	-	VFC100‑0500
M3	SC100‑0500 & SC100	-	VFC100‑0500
6‑32	SC125‑0500, SC125, SC125‑1500	SCE‑118‑236	VFC125‑0500
M4‑0.7	SC148‑0500, SC148‑0750, SC148	SCE‑118‑236	VFC146‑0472
8‑32	SC156‑0500, SC156, SC156‑1500	SCE‑118‑236	VFC156‑0500
M5‑0.8	SC180	SCE‑118‑236	VFC180‑0600
10‑24	SC172‑0500, SC172, SC172‑1500	SCE‑118‑236	VFC172‑0500
M6‑1.0	SC223‑0500, SC223‑1000, SC223	SCE‑118‑236	VFC220‑0590, VFC220‑0787, VFC223‑0720
1/4‑20	SC234‑0500, SC234, SC234‑1500	SCE‑236‑354	VFC240‑0500
5/16‑18	SC281, SC281‑2000	SCE‑236‑354	-
M8‑1.25	SC295‑0500, SC295‑125, SC295	SCE‑236‑354	VFC295‑1000 (N/S)
3/8‑16	SC355	SCE‑236‑354	VFC350‑740 (N/S)
M10‑1.5	SC375‑0750, SC375, SC375‑1500	SCE‑354‑472	VFC376‑0825
M12‑1.75	SC456‑0500, SC456‑1000, SC456	SCE‑354‑472	VFC460‑700 (N/S)
1/2‑13	SC468, SC480	SCE‑472‑591	-

N/S = Non-stock items, but are available with no tooling cost. 

Want to print this chart do you can keep it handy? Download it here in PDF format.

How to Measure Threaded Studs for the Right Masking Cap

If you don't know the thread size but can measure the diameter across the threads with calipers, use that dimension to select your cap. For a snug fit that won't fall off during powder coating, choose a cap with an inside diameter (ID) that is slightly smaller (approx. 2% to 5%) than your stud diameter. In larger sizes, a diameter that is 0.020” is often preferred. For processes where the cap is immersed in an anodizing or plating tank, a slightly smaller cap may be useful for ensuring minimal / no leakage.

Frequently Asked Questions About Caps for Masking Threaded Studs

• Can these caps withstand powder coating oven temperatures? Yes, our silicone caps are rated to withstand up to 500°F (260°C) and can often handle intermittent spikes up to 600°F. They remain flexible and won't melt or char in standard curing cycles.
• Are these masking caps reusable? Absolutely. Silicone caps are highly durable and can be reused multiple times. To extend their life and for consistently clean masking lines, we recommend cleaning the powder buildup routinely.
• How do I create a grounding area on a threaded stud? Use our VFC line of flange caps. The wide flange at the base of the cap masks a circular area around the stud, ensuring a clean metal-to-metal contact point for electrical grounding after the coating is applied. Don't see the size you need? Contact us for a custom quote - we can have short runs or large quantities designed and made. 
• What is the benefit of an expandable cap? Expandable caps (SCE series) feature an internal rib design that allows a single cap to fit multiple thread diameters. This is perfect for job shops that want to reduce their masking inventory. Watch for the potential for excess trapped air inside - some powder coaters snip a small portion at the end to allow for venting of superheated air. 
• Will these caps work in plating or anodizing tanks? Yes, silicone has excellent chemical resistance. They are ideal for Type II and Type III anodizing, as well as most plating baths including nickel and chrome. If you are using especially aggressive chemicals in your process, ask us for a sample to test first (we also carry EPDM rubber caps and plugs).
• What if my stud is longer than your standard caps? If our standard SC line is too short, we recommend using silicone tubing cut to length. You can either leave the end open or place a small cap over the tubing for a complete seal.