I think the term is quoin. Here's merriam-Webster's definition:
Main Entry: 1quoin
Pronunciation: 'koin, 'kwoin
Function: noun
Etymology: alteration of 1coin
1 a : a solid exterior angle (as of a building) b : one of the members (as a block) forming a quoin and usually differentiated from the adjoining walls by material, texture, color, size, or projection
2 : the keystone or a voussoir of an arch
3 : a wooden or expandable metal block used by printers to lock up a form within a chase
Of course the quoin used with cannon is just one wedge, where the printing quoins are a pair of wedges with a set of teeth (like a rack) turned by a quoin wrench (pinion).
It is not as elegant form of adjusting elevation as the threaded mechanisms, but it's cheap.