tender for spring for bolster friction device for wap-4 loco as per clw drg. no. 03/04/16/3 alt 06. materialgrade 50cr4v2 as per is 3195 or en-47 as per bs: 970 specn. no. is: 7906 hardness range 415 bhn to 460bhn as per drg.no. clw drg. no. 03/04/16/3 alt 06. material grade 50c specn: is: 7906 hardness range 415bhn to 460 bhn .