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Frequently Asked Questions
What does a masking cap cover?
An external feature - a thread, stud, spigot or shaft end.
It keeps the process off a surface that must stay clean.
It has to grip through handling and the process itself.
Then it must come off cleanly.
The surface should be exactly as it was before.
That is a different job from a plug, which goes into a bore.
How tight should the grip be?
Enough to stay on, not so much that removal damages anything.
Too loose and coating creeps underneath.
Too tight and removal can leave material behind in a thread.
Tapered designs accommodate a range of diameters in one part.
That also cuts the number of variants to stock.
Trialling on a sample part before a production run is worth the time.
Which material suits my process?
Choose by temperature and chemistry rather than by size.
Silicone tolerates repeated high-temperature cycles.
It does not bond to coatings, which matters at removal.
Vinyl and rubber suit lower-temperature processes at lower cost.
Plating and anodising chemistry attacks some compounds directly.
A cap that softens or reacts contaminates the part it was protecting.
Why do threads matter particularly?
Because a coated thread will not accept its fastener.
The part then gets reworked or scrapped.
It is the most common single application for these caps.
Coverage has to include the first thread at the root.
A cap stopping short leaves a coated start.
That is enough to prevent a fastener starting cleanly.
How many times can a cap be re-used?
Silicone commonly survives many cycles; vinyl and rubber far fewer.
They degrade gradually rather than failing obviously.
Hardening, discolouration and lost flexibility are the signs.
Tracking cycles is what prevents a cap failing mid-process.
One failure can cost more than the caps it saved.
Re-use is where most of the economics of silicone caps sit.
Why are they brightly coloured?
So anything left on a finished part is obvious at inspection.
A cap left in place is a defect.
Contrasting colours make it visible immediately.
It is a quality control feature rather than decoration.
Counting caps out and back in is used on critical work.
Pull tabs serve the same purpose by making removal quick enough to actually happen.
Do they survive blasting as well as coating?
Only if specified for it - blasting is a more abrasive duty.
Media strips thin material quickly at edges.
Caps intended only for coating usually will not survive.
Thicker-walled and harder compounds are made for it.
Purpose-made steel or hard rubber masking is used in some cases.
Where a part is blasted and then coated, the two stages may need different masking.