There are three types of Moteck, one with a 50mm tube one with 52mm and one with 57mm and all of them carry the same dish size recommendations, it isn't the diameter of the tube which is critical, it is what is driving it and how it is attached.
PS. Just looked at the spec foe the older Moteck SG-2100, that one has a 55mm tube, so it will possibly be a clone of the old one
http://www.satellites.co.uk/php-bin/...5&d=1112208919