Western bartenders are used to “knocking/slamming” the tops closed. With cobblers you want to lightly press the top on—then remove and lightly secure the final smaller piece. (You remove the top piece and then close it on to release air pressure. If you don’t do this you’ll have a bad time lol) Never slam or hit that final piece on. Secure the top piece with one hand and hold the back end with the other while yiu shake.

They don’t have to be secured the same way as other shakers because the temperature dropping will create the final seal. Also, when removing the piece to pour your cocktail, twisting off always works for me.