Match Masking Plugs to Common Threaded Holes
Find correct plugs for UNC/UNF/metric threads
Silicone plugs are ideal for threaded holes because they withstand up to 500F for powder coating or ecoating and are chemically resistant for electroplating and Type 2 / Type 3 anodizing. There are a variety of plugs available for thread protection for powder coating, paint, anodizing, plating, ecoating and other metal finishing processes to mask the first-thread / chamfer and/or provide a good grounding area.
Skip to the UNC / UNF / metric thread masking guide below to find the right plug quickly. For a bit of detail on blind hole vs. through hole masking, read on.
Plugs for blind holes with threads
When a thread does not go through a part, it is called a blind hole. Typically these are masked with tapered plugs (STP), alternatively with selected tapered plugs with a handle (STP-H) or if the lead-in thread requires masking, a first thread plug (VTMP) is used. Scroll to the bottom of page for our threaded hole / plugs chart, then use the links below to get the right plug to mask common UNC and metric thread sizes.
Plugs for thru holes with threads
For threaded holes that go all the way through metal - typically 1" thickness or less - then a pull plug (SPP) is often used for quick and effective masking. When the lead thread must be masked as well, a specialized pull plug with a flange at the end (SFPP) is used. Check the threaded hole / masking plugs chart below, then use the links here to get the right plug to mask common UNC, UNF and metric thread sizes.
Download the chart below in PDF format for printing / quick reference
Don't see the thread you need a plug for listed below? 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 & plugs for blind and thru holes
| Thread size |
Plugs for blind holes |
Plugs for thru‑holes |
| Tapered plug |
Tapered plug w/handle |
1st thread plug w/handle |
Pull plug w/handle |
Pull plug w/handle and flange for first thread |
| 4‑40 |
STP100 |
STP100‑H |
N/A |
SPP11 |
N/A |
| 6‑32 |
STP101 / STP101XL |
STP101‑H |
VTMP‑0107 |
SPP14 |
SFPP-0118-GREEN |
| M4‑0.7 |
STP101 / STP101XL |
STP101‑H |
VTMP‑0141 |
SPP18, SPP20, SPP21 |
SFPP-0142-PURPLE |
| 8‑32 |
STP101 / STP101XL |
STP101‑H |
N/A |
SPP18, SPP20 |
N/A |
| M5‑0.8 |
STP1012 / STP102XL |
STP102‑H |
VTMP‑0178 |
SPP22A |
SFPP‑0173‑RED |
| 10‑24 |
STP102 / STP102XL |
STP102‑H |
VTMP‑0178 |
SPP22A |
SFPP‑0173‑RED |
| M6‑1.0 |
STP103 / STP103XL |
STP103‑H |
VTMP‑0208 |
SPP30 |
SFPP‑0210‑WHITE |
| 1/4‑20 |
STP103 / STP103XL |
STP103‑H |
VTMP‑0208, VTMP‑0218 |
SPP30 |
SFPP‑0218‑BLUE, SFPP‑0230‑GREY |
| 5/16‑18 |
STP104 / STP104XL |
STP104‑H |
VTMP‑0278 |
SPP40 |
SFPP‑0285‑YEL |
| M8‑1.25 |
STP104 / STP104XL |
STP104‑H |
VTMP-0283 |
SC172 cap (nose-in / use like plug) |
SFPP‑0285‑YEL |
| 3/8‑16 |
STP106 |
N/A |
VTMP‑0336 |
SPP42, SPP43 |
SFPP‑0335‑OR |
| M10‑1.5 |
STP106 |
N/A |
VTMP‑0358 |
SPP50 |
SFPP‑0350‑PINK |
| M12‑1.75 |
STP00 |
STP00‑H |
VTMP‑0426 (non-stock) |
SPP66 |
SFPP‑0420‑GREEN |
| 1/2‑13 |
STP108 |
N/A |
VTMP‑0451 |
SPP66, SPP67 |
SFPP‑0445‑PUR |
Want to print this chart do you can keep it handy? Download it here in PDF format.
If you know the thread callout, use the chart above to find the plug size you need quickly.
How to measure threads for the right masking plug
If you don't know the thread but can meause the diameter across the threads with a set of calipers, measure that dimensions and then use a plug that is 2% to 5% larger in smaller sizes or 0.020" bigger in larger thread sizes. Note that coatings buildup, thread class or chamfer depth can affect the fit of plugs. Viadon is happy to send FREE SAMPLES of plugs for testing. Contact us for more info.
Frequenty Asked Questions about plugs for masking threaded holes
How do I mask the first thread / chamfer?
There are several plugs available to do this. For blind holes, Viadon's VTMP series has a small flange that will mask the lead-in thread along with internal blind hole threads. For through holes, Viadon's SFPP series are pull plugs with a flange at the end; pull that plug through the hole until the flange seats on the first thread for perfect masking every time.
How do I choose between a tapered plug and a pull plug?
Tapered plugs are usually the first choice for masking blind holes because they are low cost and easy to use. But for holes that go through a part, where you can see daylight on the other side, a pull plug is often faster and easier, assuming the thickness of the part is 1" or less, as most pull plugs are only 1" long. For thicker parts, two tapered plugs, one inserted on each side, may be a viable option for masking through holes in those cases. And for very shallow blind holes? Sometimes taking a pull plug and inserting it "plug first" so the tail is sticking up is a great way to keep a plug from falling out when a tapered plug does not have the right narrow diameter.
Can these plugs withstand powder coating / ecoating oven temperatures?
Yes, silicone plugs will withstand up to 500F and are reusable.
Can these plugs withstand acid baths in plating?
SIlicone plugs are often used in nickel or chrome plating, and they will withstand sulfuric acid used in anodizing as well.
What if I need a masking plug for a thread size not listed here?
Viadon not only has access to plugs we do not normally stock, but even if there is not an existing plug option, custom plugs can be made in either small or large quantities from single cavity or production cavity tooling. This can lower your overall costs by allowing for faster, more effective masking. Contact us for details.