THE PINNACLE OF PRECISION & PERFORMANCE™ ALTRA NON-MICRO FORWARD MASS SYSTEM (FMS) INSERT WEIGHT SYSTEM OFFERS FINE ADJUSTMENT OF TOTAL ARROW WEIGHT TO INCREASE F.O.C. AND IMPROVE DOWN RANGE ACCURACY. THE NON-MICRO INSERT WEIGHTS ARE DESIGNED FOR USE WITH ALL ALTRA ARROWS LARGER THAN 166 AND ARE STACKABLE FOR INFINITE WEIGHT ADJUSTMENT.