Solid Brass Line 24 Snaps are the big boys, They take a lot of force to pull apart laterally, but pop together fairly easily with angular motion. These are the same snaps I use for my men's belts and tail quick release.

Snap button (the dome shaped outer piece) width is 37/64" / 0.58 inches / 14.7mm

Choose from 4 colors and 2 lengths of posts:
Bright Brass
Antique Brass
Black Oxide
Nickel Plated (silver)

15/64" (0.2344 inches / 5.9531mm) posts
20/64" (5/16" / 0.3125 inches / 7.9375mm) posts

You will need a line 24 snap setter, available from ebay or Tandy Leather Factory. If you'd like me to include a snap setter kit with your order, please inquire about this BEFORE placing your order.

For each 1 of these you buy, you'll receive 4 parts (button, socket, stud, eyelet). Order at least 2 sets more than you need, in case you accidentally destroy a button or stud post during setting.