TM 10-3930-669-34 13-2.  MAST ASSEMBLY REPLACEMENT/REPAIR (CONT). WARNING Use care when removing or installing snap  and  retaining  rings.    Snap  and retaining rings are under spring tension   and   can   act   as   projectiles when released and could cause severe eye injury. (8) Install  roller  (69)  on  center  rail  (58)  with  spacer (68) and retaining ring (67). WARNING • Center  rail  weighs  361  lbs  (164  kg).    Attach  suitable  lifting  device  prior  to  installation  to prevent possible injury to personnel. • All personnel must  stand  clear  during  lifting  operations.    A  swinging  or  shifting  load  may cause injury or death to personnel. (9) Install two screws (66) in end of center rail (58). (10) Install two lock washers (65) and screws (64) in center rail (58). (11) Install two shims (63) and rollers (62) on center rail (58). 13-18