▁making ▁this ▁form ▁resist ant ▁to ▁de br is ▁and ▁thread ▁damage . ▁ ▁Stand ards ▁ ▁Kn uck le ▁threads ▁with ▁a ▁flat ▁ 3 0 ▁degree ▁fl ank ▁thread ▁angle ▁are ▁standard ized ▁in ▁D IN ▁ 4 0 5 ▁for ▁in ch ▁pitch es ▁and ▁diam eters ▁r anging ▁from ▁ 8 ▁mm ▁to ▁ 2 0 0 ▁mm . ▁ ▁A ▁more ▁recent ▁standard ▁D IN ▁ 2 0 4 0 0 ▁uses ▁metric ▁thread ▁pitch ▁and ▁lists ▁diam eters ▁from ▁ 1 0 ▁mm ▁to ▁ 3 0 0 ▁mm . ▁ ▁As ▁D IN ▁is ▁a ▁German ▁organization , ▁many ▁instances ▁of ▁the ▁D IN ▁thread ▁charts ▁write ▁numbers ▁with ▁a ▁comma ▁as ▁the ▁decimal ▁marker . ▁ ▁For ▁a ▁thread ▁pitch ▁p , ▁the ▁cr est ▁and ▁root ▁round ing ▁radius ▁is ▁slightly ▁less ▁than ▁p / 4 , ▁and ▁approximately ▁the ▁middle ▁third ▁of ▁each ▁thread ▁fl ank ▁is ▁flat . ▁ ▁The ▁American ▁Pet role um ▁Institute ▁( API ) ▁specification ▁ 5 B ▁lists ▁a ▁" round ▁thread " ▁for ▁tub ing , ▁often ▁referred ▁to ▁as ▁" 8 ▁round " ▁or ▁" 8 rd " ▁for ▁ 8 ▁threads ▁per ▁in ch . ▁ ▁The ▁only ▁other ▁pitch ▁listed ▁is ▁ 1 0 ▁threads ▁per ▁in ch . ▁ ▁The ▁thread ▁angle ▁at ▁the ▁fl ank ▁is ▁ 6 0 ▁degrees , ▁and ▁the ▁cr est ▁and ▁root ▁round ing ▁radius ▁is ▁approximately ▁p / 6 ▁for ▁threads ▁of ▁pitch ▁p .