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Johnny

Well-known member
Joined
Nov 15, 2009
Messages
55
Location
Hurst, Texas
When I drill and tap my frame to mount my body what would be the correct size drill, tap, and bolt? I know, real dumb, huh?[S[S

Thanks
 
If it is a box frame that you can't get inside off I like to weld another small piece of steel, maybe 1.5 inches square x 1/4 thick to the top of the frame then drill and tap down through both pieces so you have a thicker area there. 3/8 is ok but as mentioned 1/2 would be better probably. Course threads will hold better as each thread is deeper.

Don
 
Ever notice the how the thickness of a nut corresponds to the diameter of the bolt? (A 1/2" nut has 1/2" of threads.) That is because that many threads are needed to equal the strength of the bolt.

So, I you have 1/8 wall box tube, you need to add 3/8 of threads to the existing thread wall of the tube. Or weld a nut inside.

Fine threads are actually rated has having more strength than course threads.
My grade 8 chart shows 1/2-13 at 25,500 pounds minimum tensile, 1/2-20 at 28,800 pounds minimum tensile.

1/2-13 tap drill is 27/64 1/2-30 tap drill is 29/64.
 
Last edited:
Actualy by thery 1/2 bolt should have 3/4 inchs deep of thred. Fine thred bolts greater streanght. Bolt grade wont matter here because any grade of bolt will be as stong or stronger than your frame steel. get like 7/16 shoulder nuts drill hole aprox size of the sholder nut drop nut in hole weld around the sholder nut, before welding sholder nut. thead a bolt into the nut so threds dont distort.
 
I don't tap frames to thin. I weld on tabs or brackets And use 1/2" bolt & nut. Use a polylock nut or lock washer. See pic. Hope this helps.
 

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