Pipe with spigot/army mounting
First of all, a quick reminder: in a classic mounting, the mortise (the female part located in the shank) and the tenon or floc (the male part of the stem end that fits into the mortise) are cylindrical in shape. Adjustment must therefore be carried out correctly, to avoid either too tight or too loose a fit. Temperature can play an important role: a pipe made in winter in a cool workshop may have a tight fit when it returns to the warm temperatures of our apartments. The opposite can also happen! Similarly, a pipe that has just been smoked can only be disassembled once it has cooled down, but I hope everyone knows that by now...
But you'll see that with these two mounting examples, things are different...
Pipe with Army mounting.
The special feature of this mounting is that the end of the stem (tenon) that fits into the mortise is tapered. Friction is therefore much lower than in a conventional (cylindrical) assembly. What's more, the outside of the shank, at the level of the mortise, is reinforced by a metal ring (often silver).
Pipe with Spigot mounting
Like the Army mounting, the end of the stem (tenon) which is inserted into the mortise is conical; But it is, moreover, enclosed with metal (generally silver) which will make the assembly even more solid over time. The shank is always reinforced by a metal ring.
In conclusion, these two mounts will be solid and will not move over time. What's more - and this is a major advantage - the pipe can be easily disassembled to, for example, pass a pipe cleaner over it to remove excess moisture or a strand of tobacco clogging the shank. There's no need to let the pipe cool down ...