In Reply to: Bolt on horns/ drver for 4 Pi's- What Bolts? posted by Garland on January 17, 2002 at 07:17:00:
The thread pattern used on the opposing pair of mounting holes is 1/4" diameter and has 20 threads per inch. The best length I've found is usually 3/4" because a 1/2" long bolt usually only "grabs" with one or two threads, if it reaches at all, and a 1" long bolt usually bottoms out. On some horns or adapters, you might need this long of a bolt, but then again, on many of them (like the H290), you have limited space to insert the bolt, so you must use a short bolt just to get it started.
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