BSP parallel pipe threads G 1-1/4 to G 6 (ISO 228-1): pitch, major, pitch and minor diameter, class A / B limits + 6 male STEP/STL files — dimension sheet Source: Xem Studio, https://xemstudio.com/objects/bsp-parallel-pipe-threads-g-iso-228-1/ (sheet CC BY 4.0) Basis: MachiningDoctor ISO 228-1 pages (eight sizes read individually) and the ISO 7-1 sample table for G 4 to G 6; EN 10255 tube sizes for the example stubs Catalog version: 2026-10-20 Sizes: see table below - G is the parallel (cylindrical) pipe thread of ISO 228-1 (BSPP): the seal is made by a washer, bonded seal or O-ring on the face, not by the thread. G 1-1/4 and up all have 11 threads per inch (pitch 2.309 mm). External threads come in class A and the looser class B (the pitch-diameter band is 0.18 mm wide for class A on G 1-1/4 to G 2 and 0.217 mm from G 2-1/4; class B is twice that); the internal pitch diameter runs from d2 to d2 plus the class A band. - Numbers: MachiningDoctor's BSPP pages for G 1-1/4, 1-1/2, 2, 2-1/4, 2-1/2, 2-3/4, 3 and 4-1/2 (each read from its own page; the generator checks d2 = d - 1.479, d1 = d - 2.958, internal band = class A band and class B band = 2 x class A on every row). G 4, G 5 and G 6 are shown with the major, pitch and minor diameters of the ISO 7-1 sample table only (ISO 7-1 and ISO 228-1 share diameters and pitch, as Engineering ToolBox states); their class A / B limits were not read, so those cells are empty. G 1-3/4, 3-1/2 and 5-1/2 are not shown: they were not verified. One disagreement: the minor diameters from MachiningDoctor differ from the ISO 7-1 sample by 0.001 mm on some sizes (e.g. G 1-1/4: 38.953 vs 38.952). - Files: 6 male envelopes for G 1-1/4, 1-1/2, 2, 2-1/2, 3 and 4. Each is a plain cylinder at the nominal major diameter (20 mm long, an EXAMPLE length) joined to an EXAMPLE EN 10255 medium tube stub (30 mm long); the tube is larger than the thread major diameter and bored through. Threads are not modelled as helices. G 1/8 to G 1 male ends are on the 'Pipe thread envelopes' page. - Left out: G 1/16 to G 1 (on the existing pages), G 1-3/4, 3-1/2, 5-1/2 and the sizes above 6, the thread runout and undercut, the tapping drill column (MachiningDoctor shows a placeholder), internal-thread files. size TPI pitch P, mm major Ø d, mm pitch Ø d2, mm minor Ø d1, mm external d2 class A min, mm external d2 class B min, mm internal d2 max, mm external major min, mm source G 1-1/4 11 2.309 41.91 40.431 38.953 40.251 40.071 40.611 41.55 MachiningDoctor G 1-1/2 11 2.309 47.803 46.324 44.846 46.144 45.964 46.504 47.443 MachiningDoctor G 2 11 2.309 59.614 58.135 56.657 57.955 57.775 58.315 59.254 MachiningDoctor G 2-1/4 11 2.309 65.71 64.231 62.753 64.014 63.797 64.448 65.276 MachiningDoctor G 2-1/2 11 2.309 75.184 73.705 72.227 73.488 73.271 73.922 74.75 MachiningDoctor G 2-3/4 11 2.309 81.534 80.055 78.577 79.838 79.621 80.272 — MachiningDoctor G 3 11 2.309 87.884 86.405 84.927 86.188 85.971 86.622 — MachiningDoctor G 4 11 2.309 113.03 111.551 110.072 — — — — ISO 7-1 sample (shared diameters); G tolerances not read G 4-1/2 11 2.309 125.73 124.251 122.773 124.034 123.817 124.468 125.296 MachiningDoctor G 5 11 2.309 138.43 136.951 135.472 — — — — ISO 7-1 sample (shared diameters); G tolerances not read G 6 11 2.309 163.83 162.351 160.872 — — — — ISO 7-1 sample (shared diameters); G tolerances not read Files elsewhere (not hosted by Xem Studio; license as stated by the publisher): - MachiningDoctor: BSPP (G) thread basic dimensions ISO 228-1 / ISO 228-2: G 1-1/4, 1-1/2, 2, 2-1/4, 2-1/2, 2-3/4, 3 and 4-1/2 (pitch, major, pitch and minor diameter, class A / B limits) — web — Publisher's page; dimensions are facts — https://www.machiningdoctor.com/threadinfo-bspp/?tid=4711 - iTeh Standards: ISO 7-1:1982 sample: Table 1 basic dimensions of pipe threads (pitch, d, d2, d1) 1/16 to 6 — web — Publisher's page; dimensions are facts — https://cdn.standards.iteh.ai/samples/3583/8bb5ad0f36684c6cbebd554338fcde0d/ISO-7-1-1982.pdf - Engineering ToolBox: ISO 7-1 and ISO 228 pipe threads: TPI, pitch, diameters and gauge length (a) — web — Publisher's page; dimensions are facts — https://engineeringtoolbox.com/iso-threads-d_752.html - Valves Tubes Fittings: BS EN 10255 steel tube: nominal bore, OD and wall (light / medium / heavy) — web — Publisher's page; dimensions are facts — https://www.valvestubesfittings.com/data/pdf/steel-tube/bs-en10255-steel-tube-technical-specifications-weight-dimensions-pressure.pdf - Engineering ToolBox: BS 1387 steel tubes: nominal bore, OD and wall (light / medium / heavy) — web — Publisher's page; dimensions are facts — https://engineeringtoolbox.com/bs1387-steel-tubes-dimensions-d_97.html Free files (CC BY 4.0, Xem Studio; STEP + STL, 6 parts): https://xemstudio.com/files/hardware/bsp-parallel-pipe-threads-g-iso-228-1/index.json API: https://xemstudio.com/api/geometry?object=bsp-parallel-pipe-threads-g-iso-228-1