Add to Cart [English]MAINSPRING 400 DAY 21 X 50 [Francais]RESSORT MOTEUR 400J 21 X 50 X 2540 [Deutsch]ZUGFEDR. 400 TGE. 21 X 50 [Espagnol]MUELLE MOTOR 21X50 400 DIAS Now: £23.17 MSRP: Was: HOLE END CLOCK MAINSPRING 21mm x 0.38mm x 50mm Clock-grade steel. Many of M&P's mainsprings were p…