
The one I was looking at has 82mm thread, and the auto focus is faulty, but it's cheap and I can live without auto focus.
The AF failed on mine, most likely because i manually focussed without reverting to MF 'mode' (unlike my 80-400 that has a clutch system). Cost me about £35 to get it repaired, not sure it went to sigma or elsewhere, think the latter.
Its recently started to play up again, but i seem to have fixed it by switching from AF to MF and back a few times !