3M 26120, PPS Series 2.0 Adapter, Type S28, 17.5 mm Female, 19 TPI
Thread, 7100135956 
Insize 4124-20, PLAIN PLUG GAGE, H7, _20mm, 6928640316920
$47.92
Supplied with Go and No-Go gages together.
Class H7. Hardness HRC 60?2.
Standard IDIN7150-2
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