Buying sights can be confusing but we at Pistol Accents are here to help.It is our experience the following work best in most cases: +0 (6.5) works best on 9/40/357 guns except the 26,27,33 +1 (6.9) works best with 10/45 guns and the 26,27,33 Glock Number to Aftermarket Number Chart: Glock Factory 6.1 = -1 Aftermarket Glock Factory 6.5 = +0 Aftermarket Glock Factory 6.9 = +1 Aftermarket Glock Factory 7.3 = +2 Aftermarket -1 (6.1) and +2 (7.3) primarily used for sight adjustment. Sight Adjustment: Adjust the rear sight in the same direction you want the bullet impact to move. Each sight height will result in a 2"-3” change of impact @ 25 yards. Impact is low, raise rear sight. Impact is high, lower rear sight.