Conduit knockout diameters (NEMA Bulletin 71): 1/2 to 6 in trade sizes, minimum, nominal and maximum, with bushing and locknut diameters + hole gauge plates — dimension sheet Source: Xem Studio, https://xemstudio.com/objects/conduit-knockout-diameters-nema-bulletin-71/ (sheet CC BY 4.0) Basis: NEMA Engineering Bulletin No. 71 (reaffirmed 2011), Tables 71-1A and 71-1B, read twice; three Xem-drawn hole gauge plates at the nominal diameters Catalog version: 2026-10-20 Overall (mm): length 298.5, width 78.7, height 3.0 - Knockout diameters for single or concentric knockouts in enclosures (outlet boxes, panels, cabinets), by conduit trade size, from NEMA Engineering Bulletin No. 71 (issued June 1965, revised 9 Sept 2004, reaffirmed 2011), Table 71-1A. The text of the table was read twice and agreed on every row. The figures exclude any projection of breakout ears or tabs (note B). - Table 71-1B in the same bulletin gives the diameter of the flange of a metallic bushing and of the locknut covering diameter for a nonmetallic bushing (Dim. B), which sets how far the fitting overlaps the hole: bushing and locknut overlap minimums are listed per size there (for 1/2 in: 0.033 in for the metallic bushing and 0.001 in for the nonmetallic locknut covering; 3/4 in nonmetallic: 0.000). A change in the knockout diameter, bushing flange, locknut or thread dimension can make an incompatible assembly (note A); dimensions for 1/2 through 1-1/4 are from UL 514 Table 20.2 (note E). - Trade size is a name, not a dimension: 1/2 in conduit is 0.840 in OD (rigid) or 0.706 in OD (EMT), and the knockout is a larger hole (0.875 in nominal) so the fitting's thread or body passes. Conduit and EMT outside diameters are on the pages emt-conduit and rigid-imc-emt-conduit-sizes-to-4-in; the metric designator column is the identification number for the same sizes (not a millimetre size). - Files: three hole gauge plates (1/2 to 2 in; 2-1/2 to 4 in; 5 and 6 in) with a through hole at each NEMA nominal knockout diameter (inches × 25.4: 22.225 mm for 1/2 in and so on, not the rounded mm column). Use them to check a punch, a step drill or a template. Plate thickness 3 mm, 8 mm between holes and 3 mm corner radii are Xem's choices. Hole diameters are exact; open them by your process's allowance if the gauge must pass a fitting. First plate 298.5 × 78.7 mm. - Not covered: the outline of breakout ears and tabs, concentric-knockout ring diameters, and the thread major diameters (Table 71-1C) of rigid conduit and IMC (the bulletin gives them; not copied). trade size (in) metric designator knockout min (in) knockout nominal (in) knockout max (in) knockout min / nominal / max (mm, as printed) metallic bushing flange Ø B (in) nonmetallic locknut covering Ø B (in) 1/2 16 0.859 0.875 0.906 21.82 / 22.23 / 23.01 1.00 0.937 3/4 21 1.094 1.109 1.141 27.79 / 28.17 / 28.98 1.23 1.189 1 27 1.359 1.375 1.406 34.52 / 34.93 / 35.71 1.54 1.485 1-1/4 35 1.719 1.734 1.766 43.66 / 44.04 / 44.86 1.92 1.859 1-1/2 41 1.958 1.984 2.016 49.73 / 50.39 / 51.21 2.18 2.109 2 53 2.433 2.469 2.500 61.80 / 62.71 / 63.50 2.68 2.635 2-1/2 63 2.938 2.969 3.000 74.63 / 75.41 / 76.20 3.20 3.156 3 78 3.563 3.594 3.625 90.50 / 91.29 / 92.08 3.83 3.812 3-1/2 91 4.063 4.125 4.156 103.20 / 104.78 / 105.56 4.40 4.343 4 103 4.563 4.641 4.672 115.90 / 117.88 / 118.67 4.94 4.890 5 129 5.625 5.719 5.750 142.88 / 145.26 / 146.05 6.05 6.062 6 155 6.700 6.813 6.844 170.18 / 173.05 / 173.84 7.20 7.110 Files elsewhere (not hosted by Xem Studio; license as stated by the publisher): - NEMA: Engineering Department Bulletin No. 71, Knockout Diameters and Fitting Dimensions to Assure Mechanical and Electrical Continuity (Tables 71-1A, 71-1B; reaffirmed 2011) — web — NEMA publication; dimensions are facts — https://www.nema.org/Technical/Documents/Bull_71_reaffirmed_12_15_11.pdf - McMaster-Carr: Knockout bushings (per-part CAD; the standard body publishes no CAD) (free STEP/IGES per part, for your own design use; no redistribution) — STEP, IGES, PDF — McMaster-Carr site terms: personal design use, no redistribution [verify license at link] — https://www.mcmaster.com/knockout-bushings Free files (CC BY 4.0, Xem Studio; STEP + STL, 3 parts): https://xemstudio.com/files/hardware/conduit-knockout-diameters-nema-bulletin-71/index.json API: https://xemstudio.com/api/geometry?object=conduit-knockout-diameters-nema-bulletin-71