Lamp cap gauging looks like a yes/no exercise. Screw the cap into the GO gauge, try it in the NOT GO gauge, write down the result. In practice, a surprising number of arguments arise between cap makers, lamp assemblers and test labs over exactly how far a cap should enter and how much torque counts as "hand tight".
The 60061-3 gauges are a system, not a single ring
IEC 60061-3 defines the gauge sheets, and the 7006 series numbers the individual gauges. For an E27 or E14 cap you are normally dealing with several checks: a GO thread gauge for the maximum cap thread, a NOT GO or minimum-thread gauge, plus separate gauges for the contact-making surface, the overall length dimensions and the insulator profile. Each answers a different question about interchangeability in a lamp holder.
The important point is that passing the thread GO gauge does not mean the finished lamp will make contact in a holder. The axial position of the central contact and the height of the metal shell relative to the insulator matter just as much. When a batch passes thread gauging but fails an electrical continuity check in the holder, look at the length and contact gauges, not the thread again.
Torque and the "it went in" problem
Most cap gauges are used with a light, controlled torque. A cap forced into a GO ring will often go in even when it is slightly oversize, especially if the shell is thin brass and the gauge is warm. Conversely, a NOT GO gauge may catch on a burr and be mistaken for a proper refusal.
| Observation | Usually indicates |
|---|---|
| GO enters freely to the reference face | Thread size within maximum material limit |
| GO binds after two turns | Check burrs, cement on the thread, and gauge cleanliness first |
| NOT GO enters more than the permitted amount | Cap undersize; check crimp and shell deformation |
| NOT GO catches immediately | Normal; but confirm the gauge is not reversed |
| Result changes after the cap cools | Thermal expansion, or cement still curing |
Use the same technique every time. A torque-limited driver or a simple consistent hand motion, a clean gauge, and a fixed endpoint such as the reference face. Where a gauge sheet specifies a torque value, use it rather than translating it into a feeling.
Temperature is not a footnote
Brass caps and steel gauges expand at different rates, and the tolerances on an E27 cap thread are small. Gauging a lamp straight out of an ageing rack or a curing oven routinely produces a different answer from gauging the same lamp an hour later at 20 °C. Let parts and gauges reach the same ambient temperature. If production cannot wait, at least keep a reference set of caps at room temperature and check the correlation regularly.
Gauges wear in a predictable place
The first two threads of a GO ring take nearly all the contact, so that is where wear shows. A worn GO ring accepts caps that are slightly too large, and the error accumulates silently. Measure the gauge at the entry region as well as at mid-depth, and keep master caps for a quick weekly verification. A NOT GO gauge that has been dropped may have a dent that reads as a refusal, so inspect the entry edge under good light before every batch.
- Store gauges dry and lightly oiled; a rusty thread is an oversize thread.
- Keep E27, E14, B22 and GU10 gauges physically separated — mixed sets cause more errors than worn ones.
- Record gauge serial numbers on the inspection sheet.
- Quarantine any gauge involved in a disputed result until it has been re-measured.
What to write on the report
A defensible result lists the gauge sheet number, the gauge identity, the ambient temperature, the torque or method used, and the outcome for each check. "Cap OK" is not a result that survives a customer audit. When a batch sits right on the boundary, re-gauge with a second, independently calibrated set before releasing it; the cost of a second check is small compared with a container of lamps that will not seat in their holders.
Sales Team