630 is the general series number. The last digit replacing the zero is an indicator of the wheelbase length. 631 = 141", 632 = 153", 633 = 165", 634 = 183", 635 = 201". If the truck was a factory 3-axle, the letter "W" would be included in the model number, which means dual drive rear axles. The lack of a "W" indicates a single rear axle. Example ("D" = diesel engine, by the way): D632 or DW632.
("Six wheeler" and "ten wheeler" are both 3-axle trucks (tandem rears) as opposed to 2-axle trucks (single rear). All 3-axle trucks have ten wheels (dual rears). "six" and "ten" are just two ways of counting/naming the wheels on the same 3-axle truck.)
