All vehicles have many Allen screws on them. The only sensible and economical thing to do is buy 2 sets of Allen keys, usually 1/32 up to 3/8 in SAE and 1-10mm in metric. They only cost about $ 12 per set and will save you a lot of hassle if working regularly on cars.
That plug should not require an Allen wrench to remove it. Your 3/8" drive ratchet wrench should fit that plug perfectly.
It is under the seat. You need to take an Allen wrench take the seat off and you will see it.
As you are sitting on the bike, there is a panal on the right side just behind the fork. It removes with an allen wrench.
An allen wrench is sometimes referred to as a hex wrench or hex key.
7mm Allen wrench
Allen Screws.
There is no Allen wrench, I believe it is 14 mm open wrench.
An Allen wrench is a hex head wrench - a screwdriver with a handle and hexagonal head at right angles to each other.
No they are NOT the same.
Manual transmission? Look for the plug on the bottom of the differential (where the CV joints attach). It is flush with the surface and takes a 17mm "Allen wrench" or "hex key". If you don't have a 17mm Allen wrench, maybe your lug bolts are 17mm. Stick the head of one into the plug and turn it with a open-end or box-end wrench.
James Van Allen didn't invent the Allen Wrench it was William G. Allen in 1909-1910 of the Allen Manufacturing Company of Hartford, Connecticut.
To fasten and unfasten Allen screws and bolts. These fasteners have a hexagonal slot in the top into which the Allen wrench or key fits.