Take the heel of your hand and smack it on the bottom of the tin. This should form a tight seal. You don’t need to hit the tin hard, just firmly. If you’re too aggressive, you can risk breaking the glass.
Monin Shaker & Boston Glass 400ml
Professional bartenders will usually choose a Boston Shaker set due to their larger capacity as well as being faster and more efficient to work with behind a busy bar. The shaker covered with rubber plastic grip to avoid frosty tin and get slipped.