So, if you have a 12mm hole that's cracked, wouldn't you want to use the 12mm insert to fix the hole and pull the cracked material back together?
Here is my concern with the logic.
Use the 10mm insert?
If you use the 10mm insert you are indeed drilling the hole smaller to tap for the 10mm hole insert fix.
But?
Part of this fix is to repair the crack as well as give the block good threads for the main caps. I'm not confident that using a smaller insert would fix a hole that started a crack from a 12mm fastener. Would the smaller insert stabilize the crack? Dunno. Ask Lock N Stitch...
Just my thoughts on the matter.
Let's hear yours.
1982 C10 SCSWB 6.5TD, mods too extensive to list. (13.69 1/4 mile @94.6 MPH) RACE TRUCK
1982 C10 SCSWB 6.2NA, 2.73 700
1986 C10 SCLWB 6.2TD 3.73 700
1989 V20 SUB 6.2NA, 3.73 400
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1994 K20LD ECSWB 6.5TD, 3.42 80E
1995 K20 SUB 6.5TD, Wrecked, ran into by stupid teen.
1995 C3500HD DRW 6.5TD, 12' Flatbed 5.13 80E
1995 C3500HD DRW 6.5TD, 18' Rollback Wrecker 4.63 80E
1994 C20HD ECLWB 6.5TD 3.73 80E Wifes Truck.
1995 C20LD ECSWB 6.5TD 3.73 80E
1995 K20LD SCLWB 6.5TD 3.73 80E
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1997 C10 Tahoe 2Door 2WD 5.7L to 6.5 Conversion Underway