Internal vs external hub dials 4x4

[GJB]

New to 4x4 so bare with me. It seams to me that there are two different styles of hub dials one that mount directly on the hub and ones that mount with what looks like a spacer. Are these interchangeable or do you need either or per your application?

[Bigdav160]

There's a difference between 6 lug (1/2 ton) and 8 lug (3/4 ton).

there are several aftermarket branded hubs - warn, mile marker - selectro.

GM offered spicer hubs as an option otherwise the hubs were bolted to the axles (full time axle)

[MJN]

The internal style hub is where the lockout hub or drive flange components are all inside or internal to the wheel hub. 1/2 ton Dana 44's are this way, 3/4 ton Dana 44's are this way after ~1977 and all GM Corporate 10 bolts are internal hubs.
External hubs are where the lockout or drive flange is bolted onto the outside of the wheel hub, ie the big Spicer hubs on Dana 44's. Warn and Mile Marker made hubs for this application as well. This style hub was used on 3/4 ton trucks and would not fit a 1/2 ton hub/axle. The photo with the person holding the hub in their hand is an example of the external hub. These are considered weaker than internal hubs due to the design and the bolts transferring the torque to the wheel hub instead of splines inside the hub itself as internal hubs use.
The hubs are not interchangeable without changing several other parts, rotor/hub assembly, spindle, etc.