Great discussion here about the need to pay attention to detail with aftermarket and retrofit parts.
In the original post Kevin noted that the bolt was metric but with an inch size head.
My thinking is that it is a true metric M10x1.5 Class 8.8 Capscrew. It has a 16 mm hex head. Across the globe you will find M10 cap screws with either 14mm, 15 mm, 16 mm, or 17 mm hex head based on the standard used in that country.
Note that 5/8” is 15.88 mm. So a 5/8 wrench or socket is a very nice fit on a nominal size 16 mm hex head. I often use inch tools on metric or metric tools on inch hex heads when I want to slightly tighter fit.
For example, yesterday I used a 14 mm crow’s foot wrench to torque the 2 center 9/16” headed bolts on the manifold of my ‘37. I do not own an inch set of crow’s foot wrenches and the 14 mm fit snuggly on the 9/16” head (14.28 mm).
Last edited by TBUChevy; 03/10/2021 5:37 PM. Reason: Added 14mm
