If you're talking about the transmission-to-bellhousing bolts, they're 1/2" X 13. (1/2" coarse thread, 3/4" wrench size) The lower legs of the transmission will have those threads, and the bolts come through the bellhousing and screw into the transmission. If you want the strongest bolts commonly available, buy Grade 8 bolts, with 6 lines on the head. The standard bolt is a Grade 5, with 3 lines.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
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