I thought this would be easy.  It's not.  I'm trying to come up with a better idea now.

Problem:  The gearbox I have bolts up to a 1/2" plate.  There are 6" standoffs between the plate and the rear face of the engine.  Two of the standoffs are drilled to encompass a single bolt, and the other two are wide enough to contain 2 bolts each.  We planned to use bolts through all the pieces into the back of the engine.  The bolts would need to be 180mm long M10 with a 1.00mm thread pitch.  Because it will be holding the prop, I consider it prudent to specify 10.9 grade bolts (equivalent to Class8). Wilders, the local bolt specialty shop, gives me a quote of $36 each.  I'd need 6 of them.  I could get a box of 10 at $30.67 each.   Ouch!!

I could do that, crying the whole time, and may possibly have to yet; but, I think it might be smarter to explore other options first (and ask people smarter than I).   I'm thinking the best way to go would be to find a way to use standard length bolts.  For instance, for the two standoffs that have two holes, we could cut a recess into each side to uncover the drilled hole.  That would allow one bolt to attach the standoff to the engine and another to attach the plate.  But that would severely compromise the clamp-up forces that hold the whole thing together and allow it to get "wobbly".  Threaded rod or studs are possibilities, but I've not been able to find either.

Where can I find extra long, high grade metric bolts that aren't specialty order items?
What other options do I have for securely bolting a plate to the back of the engine with 6" spacer?

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