How to Choose the Right Size Silicone Masking Cap

When it comes to powder coating or other high-temp coating processes, selecting the right size silicone cap can make or break the quality of your finish.

An ill-fitting cap can lead to coating leakage, poor seals, and even product rework. Whether you're masking studs, rods, bolts, or tube ends, knowing how to size your silicone masking caps properly is key.

Applications for Masking Caps

Silicone caps are a go-to solution for protecting external features during finishing processes where precision is key. Their heat resistance, flexibility, and reusability make them ideal for a wide range of industrial applications.

Coating & Finishing Processes

Masking caps are commonly used in:

• Powder Coating – Protect threaded studs, rod ends, and tube openings from overspray and bridging.
• E-Coating – Prevent electrical current from passing through unwanted contact points, like exposed pins or terminals.
• Anodizing & Plating – Shield components from corrosive chemical baths while maintaining clean contact areas.
• Wet Paint & Spray Coating – Cover exposed ends to ensure clean lines and avoid excess paint buildup.

How to Size a Silicone Masking Cap

Choosing the correct size silicone cap is all about achieving a snug, secure fit that won't fall off during processing—or worse, allow coating to leak underneath.

Undersizing Rule of Thumb

To ensure a tight seal, the inside diameter (ID) of the masking cap should be 5% to 10% smaller than the outside diameter (OD) of the stud, pin, or tube being masked.

Example: 5% Undersize for a 0.5" Diameter Bolt

• Bolt OD: 0.500 in (12.70 mm)
• 5% Undersize: 0.500 × 0.95 = 0.475 in (12.07 mm)
• Recommended cap ID: 0.475 in (12.07 mm)

Clean, Rotate, Reuse, Replace

Silicone masking caps can typically be reused several times, depending on your coating process, but only if they're kept clean and in good condition.

Be sure to:

• Inspect plugs and caps for wear
• Rotate used and unused caps to prevent overuse of the same item
• Discard any rubber cap or silicone cap that no longer fits snugly

These practices apply directly to our silicone caps as well as silicone plugs. A simple plug-check process ensures that worn-out masks are removed from circulation and replaced with fresh inventory, maintaining masking quality and reducing defects.

Need Help Choosing?

Still unsure about your fit? At MaskingSupply.com, we offer expert guidance to help you find the perfect size silicone caps for powder coating. Contact us!