I would talk to a bolt supplier about the nuts, but from a strength standpoint, the nuts only need to stay on the bolt so it does not drop out of the hole. T-Line towers don't use friction connections and only transfer loads though shear and bearing, so it doesn't matter how big or strong the nut is as long as it keeps the bolt in the hole.

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I have been called "A storehouse of worthless information" many times.

Thanks transmissiontowers. I have a customer who wants the DH nuts for tower applications however I have spoken with 4 suppliers and importers and each one claims they do not exist. Infasco claims they exist as an offshore import (they do not manufacture) however i can find no one who can find these.

I agree with your comment on grade requirements (bolts for shear transfer only) and my customer now does as well so we will be supplying the standard grade A nuts.

If Infasco does not have or make the nuts, they probably don't exist. If you client was willing to pay for the tooling and order about 25 million nuts, someone might make them.

Sometimes customers have unrealistic desires. I work with telecom companies that put antennas on our towers and poles and I have to analyze the structure with the extra wind loading. Now, the telecom guys are used to throwing money at a problem to get what they want. Sometimes we replace a structure with a steel pole strong enough and tall enough to handle the antennas. The problem is the lead time on a steel pole is up to 20 weeks and the telecom folks want it much sooner. I jokingly tell them all they have to do is come up with a few Billion Dollars and buy the pole fabricator, put their pole at the head of the line, produce the pole, and then sell the pole company. They usually don't see my humor.

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I have been called "A storehouse of worthless information" many times.

Threaded Fasteners does stock ASTM A563 DH regular nuts. Both Nucor and St. Louis Screw & Bolt can also make them. I realize the DH nuts for ASTM A394 Type 1 bolts tend to be overkill on our transmission towers but decided to not go with a lesser grade since they are available, and for little if any higher cost.

ASTM A563 requires:
Hex Nut Grade A for A394 T0
Hex Nut Grade DH for A394 T1

"Regular" Hex nuts grade DH are not hard to find for suppliers of A394 bolts.