And the blade adjustment tool for the No.4 doesn't work on the No.5 and the special ones for the No.5 are made of unobtanium.....
Fortunately, I haven't had need to changing mine, as it was about as bang on when I bought it as I would ever expect a No.5 to be (even managed a V-bull once at 600yrds at Bisley on modern targets with my No.5.......only the once mind, but hey, for a No.5 )