- Threading Tap to Drill Bit Chart - 
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 Tap Size  	| Drill Bit Size       		|  Tap Size  | Drill Bit Size
----------------------- ----------+-----------------------------
                                  |
   8-32 NC   #29(.136") or  9/64" 		| 5/8-11 NC ----------- 17/32"
   8-36 NF   #29(.136") or  9/64" 		| 5/8-18 NF ----------- 37/64"
                                  |
  10-24 NC   #25(.150") or  5/32" 		| 3/4-10 NC ----------- 21/32"
  10-32 NF   #21(.157") or 11/64" 	| 3/4-16 NF ----------  11/16"
                                  |
 1/4-20 NC    #7(.201") or 13/64" 		| 7/8-9  NC ----------- 49/64"
 1/4-28 NF    #3(.213") or  7/32" 		| 7/8-14 NF ----------- 13/16"
                                  |
5/16-18 NC   letter "F" or 17/64" 	|   1-8  NC ------------ 7/8"
5/16-24 NF   letter "I" or  9/32" 		|   1-12 NF ----------- 15/16"
                                  |
 3/8-16 NC ---------------- 5/16" 		|   1/8" NPT ---------- 21/32"
 3/8-24 NF --------------- 21/64" 		|   1/4" NPT ----------- 7/16"
 3/8" NPT ---------- 37/64"
7/16-14 NC ---------------- 3/8" 		|   1/2" NPT ---------- 23/32"
7/16-20 NF --------------- 25/64" 		|   3/4" NPT ---------- 59/64"
1" NPT --------- 1-5/32"
1/2-13 NC --------------- 27/64" 		| 1-1/4" NPT --------- 1-1/2"
1/2-20 NF --------------- 29/64" 		| 1-1/2" NPT -------- 1-47/64"
                                  |
9/16-12 NC --------------- 31/32" 		| 14mm x 1.25 pitch (spark plug)
9/16-18 NF --------------- 33/64" 		|  use 15/32" or 12mm drill bit.



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