These chrome-plated corners are of quite heavy quality and come complete with matching screws, which are countersunk into the metal, but be aware that as a result of this you may have to make corresponding recesses in the cab unless it's relatively soft wood and the screw pressure is sufficient to press into the material.
These are the "wrap-around" types which come around the front of the cab and extend slightly into the recess with the baffle, which is a good thing and ensures they won't get pulled off if they catch in something during transport. This may however be a problem if e.g. the back panel mounts flush to the edges, not leaving enough room for the corner to sit properly.
Note however that for a standard cab, you'll need two sets (8 corners, not 4!), and for Fender blackface-style combos, only 6 are required as the sloped front panel at the top won't take the corners. All in all a very good quality addition to any budget amp that doesn't already have them, adds valuable protection and improves to look of the amp a very little cost.