Steinway changed from the
#12-36 agraffe to the 1/4-36 agraffe in 1929. All pianos with the new agraffes had a star (*) cast into the plate to indicate the new size. I don't know when the star was discontinued. In all of the Steinway factory literature/notes that I have seen there is no mention of a 7/32"agraffe. In the change order it specifically says to change the #12-36 agraffe to the 1/4-36 agraffe. This is because in the real world there is no such thing as a 7/32" machine screw or bolt. It is a term/size that we use as piano technicians because as a group we're not that familiar with machining. FYI- A machine screw is threaded from end to end and is intended to be put in a threaded hole. A bolt is used with a nut. Of course nuts can be used with a machine screw so the terms get used interchangeably. Screw sizes range from #0-80 (.060") to #12-28 (.216"). At that point they change to fractional sizes starting at 1/4" and up. 7/32" equals 0.0219" and falls between #12 and 1/4 ". You will never find this size in a catalog or hardware store because it doesn't exist (unless you're using a Harbor Freight caliper). They may say it's a 7/32" but it will be a #12 machine screw. The "36" is a thread per inch count used for agraffes and I have never seen nor heard of anything else that uses 1/4-36. Some pianos I've seen have had both sizes of agraffes. Also, don't forget that some agraffes have wide spacing of the string holes and others have narrow. And since we're on the subject- Why do we buy a 23/32 counter bore (CB) to shave the base of the agraffe? The 23/32 CB is the smallest CB that has a 1/4 hole in the end. This hole is for the pilot when it is used as a CB. But we don't use it that way. We put the stem of the agraffe into the hole. Buy a 24/32 which is 3/4 inch. Then you can use for other things. It's a much more useful size. Someone should tell the supply houses. This is piano technology dogma that no one ever thinks about or questions. I hope this is useful information.
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Glen Hart
Grand Junction CO
970-434-5558
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Original Message:
Sent: 09-18-2018 19:41
From: Karl Roeder
Subject: Agraffe thread size
Mr. Wood,
If it's from 1970 they're 1/4". As to when the switch was made I'm not exactly sure but I just put a set in an M from 1935 and they were 1/4" much to my chagrin as I had already bought a 7/32" set.
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Karl Roeder
Pompano Beach FL
Original Message:
Sent: 09-18-2018 16:52
From: Zeno Wood
Subject: Agraffe thread size
Hi gang,
Looking at getting new agraffes for a 19702 Steinway B. 7/32" or 1/4"? When did they change over?
Thanks,
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Zeno Wood
Brooklyn, NY
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