9 out of ten times its 5/8 or if its metric its a 14 if that dont work try a 9/16ths
A 35mm wrench....
21mm socket or wrench
18mm
5/8
A 10mm wrench, or if you don't have metric wrenches, a 13/32 wrench.
A 1 1/4" wrench will fit a bolt of the same size .
wrench for lug nuts on f250 is 7/8s of an inch there is a metric wrench that fits but i cant remember what size it is
10mm
The one that fits it tightly/
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.
Spark plugs use SAE and not Metric. The one that fits it is the one that fits it.
7/8