Strut size for M40B18 SOHC E30 318i 45mm vs 51mm

[twno1]

My car is M40B18 (European timing belt-driven SOHC), 1990~1991. What strut housing do I have? Is it 45mm or 51mm? I have found some discussions on this topic but the answers provided in these threads seem to be for the North American chain-driven M42B18 DOHC only.

[glnr13]

fail safe is to measure circumference with a measuring tape, then divide your measurement by 3.14. Or measuring calipers.