Hi,
I've only just seen your request as I'm looking for the tread type to replace a few missing fixings on a AH 250 I bought a while ago and had to join the site.
The dimensions of this amp (out of the rack) is Width 17 & 1/8"; Height 3 & 1/2" and the depth including the depth of the controls is 11 & 1/4".
Hope this helps,
Andy