Caps are generally used to mask studs and tube ends. Some times they can be inverted as plugs.
 
Meanwhile, don't forget to check out other finishing product categories in the following:
masking plugs masking tapes masking die-cuts

Products

Clear Silicone Caps 600F (315C)
Clear Silicone Caps 600F (315C)
Flange Caps 600F (315C)
Flange Caps 600F (315C)
Color Silicone Caps 600F (315C)
Color Silicone Caps 600F (315C)
High Temperature Vinyl Caps 350F(177C)
High Temperature Vinyl Caps 350F(177C)
EPDM Caps 350F (177C)
EPDM Caps 350F (177C)