Inch Thread Gage Pitch Diameters

(Sizes 1 9/16" Through 2")

Typical thread class usage:

A class 1A external thread and a class 1B internal thread gives a loose fit.

A class 2A external thread and a class 2B internal thread gives a normal fit.

A class 3A external thread and a class 3B internal thread gives a close fit.

Classes 1A, 2A, and 3A gages are thread ring gages to check external threads.

Classes 1B, 2B, and 3B gages are thread plug gages to check internal threads.

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Fractional Thread Size
Decimal Thread Size
Go Pitch Diameter

(P.D.)

No Go Pitch Diameter

(P.D.)

1 9/16-6 UN-2A
1.5625-6 UN-2A
1.4518"
1.4436"
1 9/16-6 UN-2B
1.5625-6 UN-2B
1.4542"
1.4648"
1 9/16-6 UN-3A
1.5625-6 UN-3A
1.4542"
1.4481"
1 9/16-6 UN-3B
1.5625-6 UN-3B
1.4542"
1.4622"
1 9/16-8 UN-2A
1.5625-8 UN-2A
1.4791"
1.4717"
1 9/16-8 UN-2B
1.5625-8 UN-2B
1.4813"
1.4909"
1 9/16-8 UN-3A
1.5625-8 UN-3A
1.4813"
1.4758"
1 9/16-8 UN-3B
1.5625-8 UN-3B
1.4813"
1.4885"
1 9/16-12 UN-2A
1.5625-12 UN-2A
1.5066"
1.5007"
1 9/16-12 UN-2B
1.5625-12 UN-2B
1.5084"
1.5160"
1 9/16-12 UN-3A
1.5625-12 UN-3A
1.5084"
1.5040"
1 9/16-12 UN-3B
1.5625-12 UN-3B
1.5084"
1.5141"
1 9/16-16 UN-2A
1.5625-16 UN-2A
1.5203"
1.5151"
1 9/16-16 UN-2B
1.5625-16 UN-2B
1.5219"
1.5287"
1 9/16-16 UN-3A
1.5625-16 UN-3A
1.5219"
1.5180"
1 9/16-16 UN-3B
1.5625-16 UN-3B
1.5219"
1.5270"
1 9/16-18 UNEF-2A
1.5625-18 UNEF-2A
1.5249"
1.5199"
1 9/16-18 UNEF-2B
1.5625-18 UNEF-2B
1.5264"
1.5329"
1 9/16-18 UNEF-3A
1.5625-18 UNEF-3A
1.5264"
1.5227"
1 9/16-18 UNEF-3B
1.5625-18 UNEF-3B
1.5264"
1.5312"
1 9/16-20 UN-2A
1.5625-20 UN-2A
1.5286"
1.5238"
1 9/16-20 UN-2B
1.5625-20 UN-2B
1.5300"
1.5362"
1 9/16-20 UN-3A
1.5625-20 UN-3A
1.5300"
1.5264"
1 9/16-20 UN-3B
1.5625-20 UN-3B
1.5300"
1.5346"
1 5/8-6 UN-2A
1.6250-6 UN-2A
1.5142"
1.5060"
1 5/8-6 UN-2B
1.6250-6 UN-2B
1.5167"
1.5274"
1 5/8-6 UN-3A
1.6250-6 UN-3A
1.5167"
1.5105"
1 5/8-6 UN-3B
1.6250-6 UN-3B
1.5167"
1.5247"
1 5/8-8 UN-2A
1.6250-8 UN-2A
1.5416"
1.5342"
1 5/8-8 UN-2B
1.6250-8 UN-2B
1.5438"
1.5535"
1 5/8-8 UN-3A
1.6250-8 UN-3A
1.5438"
1.5382"
1 5/8-8 UN-3B
1.6250-8 UN-3B
1.5438"
1.5510"
1 5/8-10 UNS-2A
1.6250-10 UNS-2A
1.5581"
1.5517"
1 5/8-10 UNS-2B
1.6250-10 UNS-2B
1.5600"
1.5683"
1 5/8-12 UN-2A
1.6250-12 UN-2A
1.5691"
1.5632"
1 5/8-12 UN-2B
1.6250-12 UN-2B
1.5709"
1.5785"
1 5/8-12 UN-3A
1.6250-12 UN-3A
1.5709"
1.5665"
1 5/8-12 UN-3B
1.6250-12 UN-3B
1.5709"
1.5766"
1 5/8-14 UNS-2A
1.6250-14 UNS-2A
1.5769"
1.5714"
1 5/8-14 UNS-2B
1.6250-14 UNS-2B
1.5786"
1.5858"
1 5/8-16 UN-2A
1.6250-16 UN-2A
1.5828"
1.5776"
1 5/8-16 UN-2B
1.6250-16 UN-2B
1.5844"
1.5912"
1 5/8-16 UN-3A
1.6250-16 UN-3A
1.5844"
1.5805"
1 5/8-16 UN-3B
1.6250-16 UN-3B
1.5844"
1.5895"
1 5/8-18 UNEF-2A
1.6250-18 UNEF-2A
1.5874"
1.5824"
1 5/8-18 UNEF-2B
1.6250-18 UNEF-2B
1.5889"
1.5954"
1 5/8-18 UNEF-3A
1.6250-18 UNEF-3A
1.5889"
1.5852"
1 5/8-18 UNEF-3B
1.6250-18 UNEF-3B
1.5889"
1.5937"
1 5/8-20 UN-2A
1.6250-20 UN-2A
1.5911"
1.5863"
1 5/8-20 UN-2B
1.6250-20 UN-2B
1.5925"
1.5987"
1 5/8-20 UN-3A
1.6250-20 UN-3A
1.5925"
1.5889"
1 5/8-20 UN-3B
1.6250-20 UN-3B
1.5925"
1.5971"
1 5/8-24 UNS-2A
1.6250-24 UNS-2A
1.5966"
1.5922"
1 5/8-24 UNS-2B
1.6250-24 UNS-2B
1.5979"
1.6037"
1 11/16-6 UN-2A
1.6875-6 UN-2A
1.5767"
1.5684"
1 11/16-6 UN-2B
1.6875-6 UN-2B
1.5792"
1.5900"
1 11/16-6 UN-3A
1.6875-6 UN-3A
1.5792"
1.5730"
1 11/16-6 UN-3B
1.6875-6 UN-3B
1.5792"
1.5873"
1 11/16-8 UN-2A
1.6875-8 UN-2A
1.6041"
1.5966"
1 11/16-8 UN-2B
1.6875-8 UN-2B
1.6063"
1.6160"
1 11/16-8 UN-3A
1.6875-8 UN-3A
1.6063"
1.6007"
1 11/16-8 UN-3B
1.6875-8 UN-3B
1.6063"
1.6136"
1 11/16-12 UN-2A
1.6875-12 UN-2A
1.6316"
1.6256"
1 11/16-12 UN-2B
1.6875-12 UN-2B
1.6334"
1.6412"
1 11/16-12 UN-3A
1.6875-12 UN-3A
1.6334"
1.6289"
1 11/16-12 UN-3B
1.6875-12 UN-3B
1.6334"
1.6392"
1 11/16-16 UN-2A
1.6875-16 UN-2A
1.6453"
1.6400"
1 11/16-16 UN-2B
1.6875-16 UN-2B
1.6469"
1.6538"
1 11/16-16 UN-3A
1.6875-16 UN-3A
1.6469"
1.6429"
1 11/16-16 UN-3B
1.6875-16 UN-3B
1.6469"
1.6521"
1 11/16-18 UNEF-2A
1.6875-18 UNEF-2A
1.6499"
1.6448"
1 11/16-18 UNEF-2B
1.6875-18 UNEF-2B
1.6514"
1.6580"
1 11/16-18 UNEF-3A
1.6875-18 UNEF-3A
1.6514"
1.6476"
1 11/16-18 UNEF-3B
1.6875-18 UNEF-3B
1.6514"
1.6563"
1 11/16-20 UN-2A
1.6875-20 UN-2A
1.6535"
1.6487"
1 11/16-20 UN-2B
1.6875-20 UN-2B
1.6550"
1.6613"
1 11/16-20 UN-3A
1.6875-20 UN-3A
1.6550"
1.6514"
1 11/16-20 UN-3B
1.6875-20 UN-3B
1.6550"
1.6597"
1 3/4-5 UNC-1A
1.7500-5 UNC-1A
1.6174"
1.6040"
1 3/4-5 UNC-1B
1.7500-5 UNC-1B
1.6201"
1.6375"
1 3/4-5 UNC-2A
1.7500-5 UNC-2A
1.6174"
1.6085"
1 3/4-5 UNC-2B
1.7500-5 UNC-2B
1.6201"
1.6317"
1 3/4-5 UNC-3A
1.7500-5 UNC-3A
1.6201"
1.6134"
1 3/4-5 UNC-3B
1.7500-5 UNC-3B
1.6201"
1.6288"
1 3/4-6 UN-2A
1.7500-6 UN-2A
1.6392"
1.6309"
1 3/4-6 UN-2B
1.7500-6 UN-2B
1.6417"
1.6525"
1 3/4-6 UN-3A
1.7500-6 UN-3A
1.6417"
1.6354"
1 3/4-6 UN-3B
1.7500-6 UN-3B
1.6417"
1.6498"
1 3/4-8 UN-2A
1.7500-8 UN-2A
1.6665"
1.6590"
1 3/4-8 UN-2B
1.7500-8 UN-2B
1.6688"
1.6786"
1 3/4-8 UN-3A
1.7500-8 UN-3A
1.6688"
1.6632"
1 3/4-8 UN-3B
1.7500-8 UN-3B
1.6688"
1.6762"
1 3/4-10 UNS-2A
1.7500-10 UNS-2A
1.6831"
1.6766"
1 3/4-10 UNS-2B
1.7500-10 UNS-2B
1.6850"
1.6934"
1 3/4-12 UN-2A
1.7500-12 UN-2A
1.6941"
1.6881"
1 3/4-12 UN-2B
1.7500-12 UN-2B
1.6959"
1.7037"
1 3/4-12 UN-3A
1.7500-12 UN-3A
1.6959"
1.6914"
1 3/4-12 UN-3B
1.7500-12 UN-3B
1.6959"
1.7017"
1 3/4-14 UNS-2A
1.7500-14 UNS-2A
1.7019"
1.6963"
1 3/4-14 UNS-2B
1.7500-14 UNS-2B
1.7036"
1.7109"
1 3/4-16 UN-2A
1.7500-16 UN-2A
1.7078"
1.7025"
1 3/4-16 UN-2B
1.7500-16 UN-2B
1.7094"
1.7163"
1 3/4-16 UN-3A
1.7500-16 UN-3A
1.7094"
1.7054"
1 3/4-16 UN-3B
1.7500-16 UN-3B
1.7094"
1.7146"
1 3/4-18 UNS-2A
1.7500-18 UNS-2A
1.7124"
1.7073"
1 3/4-18 UNS-2B
1.7500-18 UNS-2B
1.7139"
1.7205"
1 3/4-20 UN-2A
1.7500-20 UN-2A
1.7160"
1.7112"
1 3/4-20 UN-2B
1.7500-20 UN-2B
1.7175"
1.7238"
1 3/4-20 UN-3A
1.7500-20 UN-3A
1.7175"
1.7139"
1 3/4-20 UN-3B
1.7500-20 UN-3B
1.7175"
1.7222"
1 13/16-6 UN-2A
1.8125-6 UN-2A
1.7017"
1.6933"
1 13/16-6 UN-2B
1.8125-6 UN-2B
1.7042"
1.7151"
1 13/16-6 UN-3A
1.8125-6 UN-3A
1.7042"
1.6979"
1 13/16-6 UN-3B
1.8125-6 UN-3B
1.7042"
1.7124"
1 13/16-8 UN-2A
1.8125-8 UN-2A
1.7290"
1.7214"
1 13/16-8 UN-2B
1.8125-8 UN-2B
1.7313"
1.7412"
1 13/16-8 UN-3A
1.8125-8 UN-3A
1.7313"
1.7256"
1 13/16-8 UN-3B
1.8125-8 UN-3B
1.7313"
1.7387"
1 13/16-12 UN-2A
1.8125-12 UN-2A
1.7566"
1.7506"
1 13/16-12 UN-2B
1.8125-12 UN-2B
1.7584"
1.7662"
1 13/16-12 UN-3A
1.8125-12 UN-3A
1.7584"
1.7539"
1 13/16-12 UN-3B
1.8125-12 UN-3B
1.7584"
1.7642"
1 13/16-16 UN-2A
1.8125-16 UN-2A
1.7703"
1.7650"
1 13/16-16 UN-2B
1.8125-16 UN-2B
1.7719"
1.7788"
1 13/16-16 UN-3A
1.8125-16 UN-3A
1.7719"
1.7679"
1 13/16-16 UN-3B
1.8125-16 UN-3B
1.7719"
1.7771"
1 13/16-20 UN-2A
1.8125-20 UN-2A
1.7785"
1.7737"
1 13/16-20 UN-2B
1.8125-20 UN-2B
1.7800"
1.7863"
1 13/16-20 UN-3A
1.8125-20 UN-3A
1.7800"
1.7764"
1 13/16-20 UN-3B
1.8125-20 UN-3B
1.7800"
1.7847"
1 7/8-6 UN-2A
1.8750-6 UN-2A
1.7642"
1.7558"
1 7/8-6 UN-2B
1.8750-6 UN-2B
1.7667"
1.7777"
1 7/8-6 UN-3A
1.8750-6 UN-3A
1.7667"
1.7604"
1 7/8-6 UN-3B
1.8750-6 UN-3B
1.7667"
1.7749"
1 7/8-8 UN-2A
1.8750-8 UN-2A
1.7915"
1.7838"
1 7/8-8 UN-2B
1.8750-8 UN-2B
1.7938"
1.8038"
1 7/8-8 UN-3A
1.8750-8 UN-3A
1.7938"
1.7881"
1 7/8-8 UN-3B
1.8750-8 UN-3B
1.7938"
1.8013"
1 7/8-10 UNS-2A
1.8750-10 UNS-2A
1.8081"
1.8016"
1 7/8-10 UNS-2B
1.8750-10 UNS-2B
1.8100"
1.8184"
1 7/8-12 UN-2A
1.8750-12 UN-2A
1.8191"
1.8131"
1 7/8-12 UN-2B
1.8750-12 UN-2B
1.8209"
1.8287"
1 7/8-12 UN-3A
1.8750-12 UN-3A
1.8209"
1.8164"
1 7/8-12 UN-3B
1.8750-12 UN-3B
1.8209"
1.8267"
1 7/8-14 UNS-2A
1.8750-14 UNS-2A
1.8269"
1.8213"
1 7/8-14 UNS-2B
1.8750-14 UNS-2B
1.8286"
1.8359"
1 7/8-16 UN-2A
1.8750-16 UN-2A
1.8328"
1.8275"
1 7/8-16 UN-2B
1.8750-16 UN-2B
1.8344"
1.8413"
1 7/8-16 UN-3A
1.8750-16 UN-3A
1.8344"
1.8304"
1 7/8-16 UN-3B
1.8750-16 UN-3B
1.8344"
1.8396"
1 7/8-18 UNS-2A
1.8750-18 UNS-2A
1.8374"
1.8323"
1 7/8-18 UNS-2B
1.8750-18 UNS-2B
1.8389"
1.8455"
1 7/8-20 UN-2A
1.8750-20 UN-2A
1.8410"
1.8362"
1 7/8-20 UN-2B
1.8750-20 UN-2B
1.8425"
1.8488"
1 7/8-20 UN-3A
1.8750-20 UN-3A
1.8425"
1.8389"
1 7/8-20 UN-3B
1.8750-20 UN-3B
1.8425"
1.8472"
1 15/16-6 UN-2A
1.9375-6 UN-2A
1.8266"
1.8181"
1 15/16-6 UN-2B
1.9375-6 UN-2B
1.8292"
1.8403"
1 15/16-6 UN-3A
1.9375-6 UN-3A
1.8292"
1.8228"
1 15/16-6 UN-3B
1.9375-6 UN-3B
1.8292"
1.8375"
1 15/16-8 UN-2A
1.9375-8 UN-2A
1.8540"
1.8463"
1 15/16-8 UN-2B
1.9375-8 UN-2B
1.8563"
1.8663"
1 15/16-8 UN-3A
1.9375-8 UN-3A
1.8563"
1.8505"
1 15/16-8 UN-3B
1.9375-8 UN-3B
1.8563"
1.8638"
1 15/16-12 UN-2A
1.9375-12 UN-2A
1.8816"
1.8755"
1 15/16-12 UN-2B
1.9375-12 UN-2B
1.8834"
1.8913"
1 15/16-12 UN-3A
1.9375-12 UN-3A
1.8834"
1.8789"
1 15/16-12 UN-3B
1.9375-12 UN-3B
1.8834"
1.8893"
1 15/16-16 UN-2A
1.9375-16 UN-2A
1.8953"
1.8899"
1 15/16-16 UN-2B
1.9375-16 UN-2B
1.8969"
1.9039"
1 15/16-16 UN-3A
1.9375-16 UN-3A
1.8969"
1.8929"
1 15/16-16 UN-3B
1.9375-16 UN-3B
1.8969"
1.9021"
1 15/16-20 UN-2A
1.9375-20 UN-2A
1.9035"
1.8986"
1 15/16-20 UN-2B
1.9375-20 UN-2B
1.9050"
1.9114"
1 15/16-20 UN-3A
1.9375-20 UN-3A
1.9050"
1.9013"
1 15/16-20 UN-3B
1.9375-20 UN-3B
1.9050"
1.9098"
2-4 1/2 UNC-1A
2.0000-4.5 UNC-1A
1.8528"
1.8385"
2-4 1/2 UNC-1B
2.0000-4.5 UNC-1B
1.8557"
1.8743"
2-4 1/2 UNC-2A
2.0000-4.5 UNC-2A
1.8528"
1.8433"
2-4 1/2 UNC-2B
2.0000-4.5 UNC-2B
1.8557"
1.8681"
2-4 1/2 UNC-3A
2.0000-4.5 UNC-3A
1.8557"
1.8486"
2-4 1/2 UNC-2B
2.0000-4.5 UNC-3B
1.8557"
1.8650"
2-6 UN-2A
2.0000-6 UN-2A
1.8891"
1.8805"
2-6 UN-2B
2.0000-6 UN-2B
1.8917"
1.9028"
2-6 UN-3A
2.0000-6 UN-3A
1.8917"
1.8853"
2-6 UN-3B
2.0000-6 UN-3B
1.8917"
1.9000"
2-8 UN-2A
2.0000-8 UN-2A
1.9165"
1.9087"
2-8 UN-2B
2.0000-8 UN-2B
1.9188"
1.9289"
2-8 UN-3A
2.0000-8 UN-3A
1.9188"
1.9130"
2-8 UN-3B
2.0000-8 UN-3B
1.9188"
1.9264"
2-10 UNS-2A
2.0000-10 UNS-2A
1.9330"
1.9265"
2-10 UNS-2B
2.0000-10 UNS-2B
1.9350"
1.9435"
2-12 UN-2A
2.0000-12 UN-2A
1.9441"
1.9380"
2-12 UN-2B
2.0000-12 UN-2B
1.9459"
1.9538"
2-12 UN-3A
2.0000-12 UN-3A
1.9459"
1.9414"
2-12 UN-3B
2.0000-12 UN-3B
1.9459"
1.9518"
2-14 UNS-2A
2.0000-14 UNS-2A
1.9519"
1.9462"
2-14 UNS-2B
2.0000-14 UNS-2B
1.9536"
1.9610"
2-16 UN-2A
2.0000-16 UN-2A
1.9578"
1.9524"
2-16 UN-2B
2.0000-16 UN-2B
1.9594"
1.9664"
2-16 UN-3A
2.0000-16 UN-3A
1.9594"
1.9554"
2-16 UN-3B
2.0000-16 UN-3B
1.9594"
1.9646"
2-18 UNS-2A
2.0000-18 UNS-2A
1.9624"
1.9573"
2-18 UNS-2B
2.0000-18 UNS-2B
1.9639"
1.9706"
2-20 UN-2A
2.0000-20 UN-2A
1.9660"
1.9611"
2-20 UN-2B
2.0000-20 UN-2B
1.9675"
1.9739"
2-20 UN-3A
2.0000-20 UN-3A
1.9675"
1.9638"
2-20 UN-3B
2.0000-20 UN-3B
1.9675"
1.9723"
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