A part on my recently purchased suspension called for a 10mm allen wrench in the instructions. Despite the allen key seeming to be too small, I tried it anyways and of course sheared the inside of the bolt (hopefully not so bad as to be unusable).
After this I purchased an 11mm allen wrench, this is too large and won't in fact fit in the bolt at all.
The bolt is integrated into the suspension and cannot be replaced. I am totally baffled, is the part simply defective? What other size options might I have?
EDIT: To hopefully address some of the comments below. The car is a 2008 mazdaspeed3. The part is a spring perch for the rear springs on an aftermarket coilover setup. The bolt itself allows the perch to be raised or lowered - raising or lowering the car. One solution to this is to literally dismantle everything (in which case the adjustment can be done by hand).
I uploaded a video that will helpfully clarify the situation. (photos really didn't illustrate the issue well
(Sorry for the crappy video, I was filming with an iphone under a car with about 6" of clearance)