3/8" which is the same as 9 mm. This is probably the reason it was impossible to buy a 9 mm. to fit.
You need a 3/8 Allen Wrench
Metric Allen wrench.
3/8"
use an Allen wrench not a socket or open or box wrench.
Most likely for this type of van is a 3/8 Allen wrench.
It should be a 3/8" Allen wrench.
You need a 3/8 Allen key.
I believe that is a 3/8 Allen key.
it takes a 7mm Allen wrench to remove calipers on 2003 ford focus.
t-60
7mm Allen
Most likely a 3/8 Allen, but 15 mm wrench is possible.