There are two different threads for the two different speedo cable nuts, two different gear ratios and the type for Panteras uses skew gears while the type for Mangustas and very early Panteras uses bevel gears. All this info is in the TBS which EVERY owner should have.
As John said, be SURE you get the correct one for your car. The gear ratio and ZF p/n are stamped on the end. They can be lubed a bit by submerging in oil for several days. OEMs likely have no lube left, only dust. When I repair broken ones, I add a zerk fitting.