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Frequently Asked Questions
How does a plug differ from a cap?
It goes into a bore rather than over a feature.
Tapped holes, ports, drillings and machined bores are the targets.
That inward fit changes what matters.
A plug has to seal the opening rather than cover it.
Sealing is the requirement people underestimate.
A plug that merely occupies a hole lets the process creep past its edge.
Why do tapered plugs dominate?
Because one part seals across a range of hole sizes.
Pushed in until they seat, they seal at whatever diameter they meet.
One plug therefore covers several hole sizes.
The number of variants held falls sharply.
That matters for stocking and for picking errors.
Straight-sided plugs seal only at their own diameter.
Does depth matter as well as diameter?
Yes, and blind holes are where it catches people out.
A plug bottoming out before sealing at the mouth leaves a path in.
The process then reaches the surface being protected.
In through-holes a plug pushed too far is hard to retrieve.
Plug length has to suit the hole depth.
Checking on a sample part before a run avoids both problems.
How are plugs retrieved?
By a pull tab or a protruding head, which is worth specifying.
A plug pushed fully in with neither is genuinely awkward to remove.
Tools used to dig one out can damage the bore.
Tabs make removal quick enough that it actually happens.
They cost slightly more and repay it immediately.
Bright colours make any that remain visible at inspection.
What if a plug is left in?
It is a real defect that reaches customers.
A plug inside a threaded hole prevents the part being assembled.
One inside a port can block a system.
Counting plugs out and back in is used on critical work.
Bright colours and tabs both reduce the risk.
It is a more common problem than the small size of the parts suggests.
Which material should I use?
The one that suits the process temperature and chemistry.
Silicone handles high-temperature cure cycles.
Vinyl and rubber suit lower-temperature work at lower cost.
Plating and anodising chemistry attacks some compounds directly.
A plug that softens or swells can become impossible to remove.
One that reacts contaminates the bore it was protecting.
Can they be re-used?
Silicone plugs commonly survive many cycles.
They degrade gradually rather than failing obviously.
Hardening and loss of flexibility affect the seal first.
A plug that no longer seals is worse than no plug at all.
Inspecting on removal catches degradation early.
Tracking cycles is what makes re-use a saving rather than a risk.