You can use 3/8" bolts, nuts, and lock washers...I would use no less than a grade 10. There will be "slop" in the hole fitments cause 3/8" is slightly smaller than a 10mm.
I'm looking to get ARP's:
Bolts:
10x1.25, 35mm long, 12mm wrench size...part #'s 663-1004 (hex), 673-1004 (12 point)
Nuts:
10x1.25 12mm wrench size...part #'s 300-8344 (12 point, std head), 300-8343 (12 point, small collar)
Likely will have to use the 12 point bolts due to the recess in the driveshaft flange...the 12 point head is round with a collar; the hex head will likely not fit in the recess, and if it does, you won't be able to get a good grip with a wrench. The std diameter 12 point nuts should be fine...there is no recess on the differential side.
The stock bolt is a hex head (Toyota says a Grade 10), but also has a round collar...just measured it...it's 15mm in diameter. I gotta call ARP tomorrow and see what the head diameter is on the above 12 point bolts. If they fit, it will be a very good bolt to use...ARP says they are heat-treated 8740 chrome moly bolts (black oxide finish) and are nominally rated at 170,000 psi tensile strength. That's a substantial extra margin of safety.
But, as with everything ARP sells, I'll bet they are gonna cost $5-6 each for the bolts and $4-5 each for the nuts. Probably in the $50 range for all. Then again, you gotta think about your shiny, new aluminum driveshaft whipping like an egg beater around the under carriage if these bolts give away.
