I think all Ohlins shocks are the same size? If so the the tool measures 55mm point-to-point or 60mm to the inside, however they are not a full 'circle' and so the diameter of the adjuster nut is quite a bit bigger than that. I've got a generic 55-60mm C spanner that will fit (pull only) but it is quite a bit smaller than the genuine Ohlins spanner. Best thing about the Ohlins spanner is that it works as a 'push-pull' as it has a tooth at both ends which helps with the limited access on my bikes, so it's worth getting the proper tool if you're planning on using it regularly. IIRC they're not that expensive, I got one from Harris Performance and then got another included with an Ohlins shock that I bought, again from Harris.
Both ways, the one I got from Harris is branded Ohlins. Makes it easier to get in, I don't know what a Monster 1200 is like but there's not much room on either of mine, especially the 916.
Cheers I ordered an ohlins one from BG. There’s room on the left side of the bike to access the shock ok
I have tried to unstick the preload nuts on my 748 on two occasions with the shock fitted, both of which resulted in shredded knuckles and damaged frame paint. I now remove the shocks of the 748 and 999 and adjust them on the bench. 5 minutes to get them off using an Abba stand, a block of wood and 5 minutes to refit. Removing the shock is two bolts one of which requires a long reach 8mm allen bit on the socket wrench, if your bike is designed the same way it really is the easiest and least risky way to loosen the nuts (and you can give the shock a thorough clean).
