Backstrap sleeve slides down over the top of the magazine and fills the gap between the bottom of the grip frame and the base of the magazine. This mid-sized sleeve for backstrap 2 is for your Springfield XD-S with a 3.3"-4" barrel chambered in 45 ACP.
Specifications:

Caliber	45 Automatic Colt Pistol (ACP)
Capacity
Finish	Black
Model	XD-S
Material	Polymer
Type	Magazine Sleeve
Model Fit	XD-S
Brand Fit	Springfield
Max Capacity	0