Sam at Saber supplied me with a 20# steel crush plate for my RV-7 with a 180hp engine and Catto 3-blade prop. The standard manufacture technique is to over-drill the bolt holes for good clearance by 1/64" as I recall. However, this allows for a LOT of play when installing the crush plate. I found it impossible to get the thing adequately centered. Vibration was noticable, even after prop balancing, and I'm sure I would have to rebalance after every prop R&R.
At my request, Sam drilled a new set of holes between the original holes to nominal bolt size. The AN prop bolts are actually 3 to 4 thousand'ths under nominal size. We both thought I might have to do a little reaming and/or dressing the bolts to fit through the really thick crush-plate, but I did not. Bolts with a little wax just slid right in with essentially no play. Everything else about the Sabre spacer is made to such exacting tolerance, all bolts engaged threads by hand with very little drag while spinning in to tight.
Prop has not yet been rebalanced, but it runs noticeable smoother. And, I'm comforatable that I will not need to rebalance after prop R&R, since there seems to be zero play in the crush plate with the bolts engaged.
Kudos to Sam at Sabre for quick turn-arounds and working with me at no additional charge to get this done.
BTW. To anyone building a 7 with an IO-360 and lightweight prop. Just get the 20# steel crush plate right out of the box. You're gonna need it. And if possible, get Catto to fit the carbon fiber spinner front bulkhead for the much thicker than standard crush plate. Modifying and centering the spinner with the new crush plate was no fun!