ASME B1.1 Screw Thread Classes

Question

ASME B1.1 Screw Thread Classes

DCowles (Mechanical)

(OP)

31 Aug 04 12:45

I'm qualifying a new source (distributor) for our fasteners. When doing a First Article on some #4 and #6 screws, they failed the "Go" gauge for 2A fit. The distributor says I can expect that because of the "zinc" plating. He says they are 2A before plating. My answer was one of total confusion. If what he's telling me were correct, I could even expect to get a "blob" of plating. I would say if I specify a 2A fit and they advertise a 2A fit, I should get a 2A fit. I'm about to have a "fit" fit.

Can anybody help me with this?

thanks,
Dean

ctopher (Mechanical) · Answer 1 · 2004-08-31 12:56:24

For 20 years I have never seen that problem. Maybe check the Go gage. If I find something on this I'll get back to you.

DCowles (Mechanical) · Answer 2 · 2004-08-31 14:10:40

Thanks ctopher. The Go gage belongs to the supplier. I checked the calibration tag and all was current.

I believe the truth is this: The fasteners are "pacific rim commodities" and are treated without any real urgency to meet spec. but only to meet low cost goals. We american manufacturers have learned to accept this and won't push back for fear of the cost increases. I personally am pushing back through my distrubutor so that I can get a fastener that I can count on for fit. The "cost of quality". Any comments?
dean

unclesyd (Materials) · Answer 3 · 2004-08-31 22:40:20

There is no problem with your gage.

A plated 2A bolt, maximum dimensions apply to the bolt before plating, while the maximum dimensions after plating are Class 3A.

ctopher (Mechanical) · Answer 4 · 2004-09-01 10:16:52

I think unclesyd is correct. I found this too.

Kenneth (Aerospace) · Answer 5 · 2004-09-05 23:10:25

http://www.greensladeandcompany.com/pdf/Threads-Pr...

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ASME B1.1 Screw Thread Classes