3/8-16 x 1.5-ish long bolt, flange nut, and 3/8 flat washer.
Thread flange nut onto bolt as far as it will go, flange facing away from the bolt head.
Remove too-damn-short OEM battery bolt from cable assembly. Wire-brush BOTH SIDES of the battery cable terminal, and the lead battery terminal also. Battery terminal must look "bright silver" not black, and not fuzzy green. Force washer into rubber insulator around cable end on the bolt/nut side of the terminal (not the battery side.) Newer vehicles have removable hard-plastic insulators, earlier ones use a permanently-attached rubber insulator. (The washer is not important except to space the nut farther out for tool access. If you can cram TWO washers in there, even better.)
Thread aftermarket bolt (with nut) through the washer, through the cable end, and into battery finger-tight. The nut should still be loose.
Hold the bolt, tighten nut to clamp cable end to battery. Since bolt is fully-threaded into the battery, it'll hold slightly more torque than the OEM battery bolt. This is essentially the same concept as head studs or main studs in an engine.
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Bolt sticking out kinda ruins the "sealed" part of the sealed-terminal battery system, but allows easy access for clamping jumper cables onto battery terminals for jump-starting other vehicles.
The "official" torque for the OEM side-terminal battery bolts is 11 ft/lbs. Even I, who is decidedly torque-wrench-crazy, do not torque the battery cable bolts. Maybe I should start...