Armature Lock Ring - Early 4" & MOD, Early 4-1/2" & MOD, OSGR & PMGR - 10.5mm ID x 15.6mm OD x 2.7mm Thick (3124, 3128, 3131, 3132, 3135, 3139, 3142, 3145, 3148, 3149, 3151, 3152, 3153, 3154, 3155, 3156, 3157, 3158, 3160, 3165, 3168, 3169, 3172, 3174, 3175, 3176, 3179, 3180, 3181, 3185, 3187, 3188, 3189, 3191, 3196, 3198, 3207, 3208, 3209, 3210, 3211, 3212, 3264, 6674, 6676, 6677)