Having not worked on many metric cars that had Allen heads, I am a very poor judge of size. I can guess at SAE but not metric. In my chasing down problems on my car a trick I use is to take open ended wrenches and compare the flats on the allen head to the flats on the wrenches. When I find one that the flats look the same, well that would be the allen wrench size you need. I hope this helps.

Rick

1982 300D Turbo
1966 TR4A IRS
1966 TR4A LA