The one that fits tightly in the Allen socket. -Any real artisan or mechanic has a set of SAE and a set of Metric Allen keys.
8mm
Torx or Allen wrenches get more torque (pressure) on the bolt.
Usually a 1/8 Allen key
57rc
There may be an Allen wrench to turn the shaft when jammed. There is not normally any other wrench.
9mm Allen wrench
You should use a 4mm allen wrench to adjust the guitar truss rod.
I think that uses a 7mm Allen wrench.
You need a torx type socket. If you use an Allen wrench...you will strip out the inside of the bolt.
7mm Allen wrench
The recommended allen wrench size for bike pedals is typically 6mm.
The size of the allen wrench needed for bike pedals is typically 6mm.
That is a 3/8 Allen.
I believe that is a 7mm Allen.
To determine the size of the rounded Allen wrench needed for the task, measure the diameter of the screw head or the hole it fits into. Match this measurement to the corresponding Allen wrench size.
The size of the m6 Allen wrench needed for this task is 6 millimeters.
You need 7/64".