It's a mixed bag. The majority of the photos are of plaid brooches which only pipers wear nowadays. The width of the material crossing over itself is enough to hold the brooch where it is. You can use a solid body brooch like a Glencoe, close the clasp around the folded plaid and wedge the top edge of the brooch over the epaulet. That doesn't work with an open work plaid brooch like a stag's head, thistle, St Andrew, or rampant lion where the bottom half of the brooch shows the tartan and the top half shows the epaulet.

I used to take a large safety pin and pin it vertically 2 or 2-1/2 inches below the epaulet with the coil or eye on top. Then I open the brooch, thread the pin through the coil, lay the plaid on top, and close the brooch over the plaid. It left a hole, but a relatively small one. The last time I wore one, I just used an Inverurie brooch with a small-bore pin and pinned the plaid right to my epaulet, but I have a plain flat strap instead of a braid.

If anyone has ever threaded the pin of their clasp through a braided epaulet, post with your experience.