Butt spacer kit Fits Air Arms S400 MPR 10-meter air rifle Fits S510 XS Sporter air rifle Includes 3 spacers of different thicknesses and 3 sets of screws of different lengths Create the perfect length of pull (LOP) with these butt spacer inserts. Made for the Air Arms S400 MPR 10-meter air rifle, these inserts come in three thicknesses and different screw lengths to attach one, two or all three spacers. Ideal for clubs that have more than one size shooter using the S400 MPR or S510 XS Sporter air rifles. Also useful if the air gun is used by one shooter who's still growing.