▁ ▁Both ▁the ▁thread ▁angle ▁and ▁round ing ▁radius ▁are ▁more ▁like ▁ordinary ▁ISO ▁threads ▁than ▁D IN . ▁ ▁For ▁ 0 . 1 2 5 ▁in ch ▁thread ▁pitch ▁( 8 ▁threads ▁per ▁in ch ), ▁the ▁API ▁round ▁thread ▁root ▁radius ▁is ▁ 0 . 0 1 7 ▁in ch , ▁and ▁the ▁cr est ▁radius ▁is ▁ 0 . 0 2 0 ▁in ch . ▁ ▁API ▁threads ▁t aper ▁at ▁ 3 / 4 ▁in ch ▁of ▁diameter ▁per ▁foot ▁of ▁length . ▁ ▁Many ▁kn uck le ▁threads ▁follow ▁neither ▁the ▁D IN ▁nor ▁API ▁standards , ▁and ▁are ▁custom ▁designed ▁and ▁fabric ated ▁for ▁the ▁particular ▁application . ▁ ▁App lications ▁ ▁This ▁thread ▁form ' s ▁good ▁de br is ▁toler ance ▁is ▁the ▁source ▁of ▁its ▁use ▁in ▁oil fields , ▁where ▁it ▁provides ▁a ▁leak - free ▁connection ▁in ▁field ▁use . ▁ ▁Many ▁European ▁autom ob iles ▁use ▁a ▁kn uck le ▁thread ▁for ▁their ▁" t ow ▁eye ," ▁an ▁external ▁thread ed ▁re cess ▁where ▁a ▁steel ▁to wing ▁lug ▁can ▁be ▁fitted . ▁ ▁For ▁example , ▁some ▁Por sche ▁cars ▁use ▁D IN ▁ 4 0 5 ▁R d ▁ 2 0 ▁x ▁ 1 / 8 ", ▁and ▁some ▁B MW ▁use ▁a ▁thread ▁similar ▁to ▁D IN ▁ 4 0 5 ▁R d ▁ 1 6 ▁x ▁ 1 / 8 ". ▁ ▁Other ▁applications ▁use ▁a ▁kn uck le ▁thread ' s ▁rounded ▁edges ▁to