The SIG SAUER X-Ray3 Pistol Sight Set features a green #8 front sight and white U-notch rear #8 sight. The higher the front size number (i.e. #6), the lower the height of the sight. For the rear sight, the higher the number (i.e. 8), the higher the height of the sight. This set is compatible with the P320, P938, P238, P229, P226, P220, P227, and P225.
SIG Sauer numbers their sight so that a smaller number will lower the Point of Impact (POI) relative to the Point of Aim (POA). So, if you start with front and rear sights that are both #8s, by changing either one of them to a #6 will drop the POI by roughly 1.5 onches.