I have been looking to get a mount of my 100-400, and various sources claim different ones fit. I thought it may be of interest/use to others, to compile a list, that once and for all clears it up.
Sources include this web site, other photographic sites, the font of all knowlege (ebay) etc.
From what I can gather Canon do three tripod mounts the A , B and C, either in (B)lack or (W)hite. There is also an adaptor for the B to make it fit smaller lenses
A=66mm dia
EF 80-200mm f/2.8L USM
EF 70-200mm f/4L USM
EF 70-200mm f/4L IS USM
EF 200mm f/2.8L USM
EF 300mm f/4L
EF 400mm f/5.6L USM
B=78mm
70-200mm f/2.8 USM
70-200mm f/2.8 IS USM
Canon EF 100-400mm f/4.5-5.6L IS USM
B+adaptor = 72mm
EF 100mm f/2.8 Macro USM
MP-E 65mm f/2.8 1-5x Macro Photo
EF 180mm f/3.5L Macro USM
C=82mm
Canon EF 35-350mm f/3.5-5.6L USM
Canon EF 28-300mm f/3.5-5.6L IS USM
I also found mention of this one, on one site
A II(W) for 70-200mm f4 usm
If you have any additions or corrections, please post up, and I will edit this post.

