There are two totally different designs that Lee calls a "Factory" crimp die. One is used mostly for rifle bottle-necked cartridges and uses a collette (fingers) to press the case mouth into the bullet. This one is not case length sensitive and you don't need to have canelure in the bullet.
The other design is for straight-walled pistol cartridges, and is just a typical crimp die, with a separate removable "collar" piece that does the actual crimping (this is the only piece of the die hardened) and the addition of the carbide sizing ring. Since your 357 Sig is a bottle-necked pistol cartridge, I am not sure which design you will get, it's pretty short for the collette design to work properly and it's a pistol cartridge, but it is bottle-necked so you could get either design I suppose.

I just got it yesterday and it's a new die called (Lee Bottle Neck Pistol Factory Crimp Die)I haven't had much chance to use it yet.

Here's a picture of the instructions.

I have one in all 7 pistol calibers I reload.
Best thing since taper crimp.
Rounds fall in & out of check gages.
Haven't had a FTF since switching.
Anyone that says they are no-good doesn't know how to use them.

I've never used one for the bottle necked pistol cartridges and can't read the instruction sheet Eagle Guns posted above, but they appear to be based off of the rifle FCD looking at the pictures on their web site.

I have the Lee FCD in 357 Sig. It works great, however it does not have a carbide resizeing ring. It is like the Rifle FCD in that it crimps only. Br aware that it is possible to over crimp a 357 Sig Case using a FCD and collapse the shoulder. Ask me how I know.

I just love simple logic.