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Frequently Asked Questions
How do I know which format I need?
By the shape of what is being protected.
A cap goes over an external feature such as a thread or a stud.
A plug goes into a bore, a port or a tapped hole.
A disc or shape covers a flat face that suits neither.
Most components need a combination rather than one type.
Working through the part feature by feature is how the list gets built.
What decides the material rather than the format?
The process, and it is a separate decision from the shape.
Format follows the geometry of the part.
Material follows the temperature and chemistry it must survive.
The two decisions are made independently and both have to be right.
A correctly shaped cap in the wrong compound still fails.
Getting the shape right and the material wrong is the commoner of the two errors.
How many variants should be stocked?
Fewer than the number of features, because tapered designs cover ranges.
A tapered plug seals across several hole sizes.
A tapered cap grips a range of diameters.
That collapses a long list into a manageable one.
Fewer variants also means fewer picking errors on the line.
Standardising deliberately is worth doing before a large order rather than after.
Can masking caps be re-used?
Silicone ones commonly survive many cycles, and that is a real economy.
They degrade gradually rather than failing obviously.
Tracking how many cycles they have been through therefore matters.
Hardening, discolouration and loss of flexibility are the signs.
Vinyl and rubber generally tolerate far fewer cycles.
A degraded cap that fails mid-process costs more than the caps it saved.
What stops a plug being left in?
Pull tabs and high-visibility colours, which are quality measures rather than conveniences.
A masking plug shipped inside a threaded hole is a genuine defect.
Bright colours make anything left behind obvious on inspection.
Tabs make removal quick enough that it actually gets done.
Counting caps out and back in is used on critical work.
It is a more common problem than the small size of the parts suggests.
Do caps and plugs mask the same things?
No - a cap goes over an external feature, a plug goes into a bore.
Caps protect threads, studs, spigots and shafts.
Plugs protect tapped holes, bores and ports.
Discs and shapes mask flat areas that neither suits.
Tape is used for irregular areas but is slower to apply.
Most components need a combination rather than one type.
Do they need to withstand blasting as well?
Shot and grit blasting is a different and more abrasive duty than coating.
Media strips thin material quickly at edges.
Thicker-walled and harder compounds are specified for it.
Caps intended only for coating usually will not survive.
Blast masking sometimes uses purpose-made steel or hard rubber instead.
Where a part is blasted and then coated, the two stages may need different masking.