The pictured hub is a 322 hub, as Vandy said, but it has been hacked to kinda-of accept a later IT-type speedo drive.
The 322 hubs were fitted to RT2MX, DT2MX, all MX250/360/400, YZ250/360A, YZ250/360B, YZ125/250/400C, YZ125X, and the first year or two of TT500s.
The 1K7 hub is identical, but has the three speedo prong drives and is missing the nine little webbs on the non-brake side.
The 2A6 hub (early monoshock DT125/175) is also identical, but has no speedo drive prongs and slighlty different webbs inside the brake drum.
And to be a complete train spotter, the YZ-K hubs (sorry code forgotten - 23X?) are all the same dimensions but look different from the outside.
FWIW, my MX250A went through scrutiny at the Nationals with a 1K7 front hub - and the scrutineer definitely noticed (and stirred me up about it, the bastard!).