manual metal arc welding electrode class a1 type of coating medium size 3 15 mm dia x 350 mm length specification irs m 28 2020 version 1 0 code er4112 medium coated as per is 814 2004 r eaffirmed 2021 sixth revision incorporating 02 amendment warranty period 12 months after the date of delivery quantity tolerance 5 age item category normal total po value variation permitted max 8 lacs