US round and octagon ceiling boxes (3-1/2, 4 in): size, cubic inches, fixture screw spacing — dimension sheet Source: Xem Studio, https://xemstudio.com/objects/ceiling-boxes-us/ (sheet CC BY 4.0) Basis: Hubbell RACO, Southwire, Allied Moulded and ABB Steel City sheets; only printed numbers Catalog version: 2026-10-20 Overall (mm): length 101.6, width 101.6, height 2.0 - US round and octagon ceiling / fixture boxes, 3-1/2 and 4 in: the sizes and cubic inches the makers print, and the two screw spacings that are printed in words: 3-1/2 in between fixture ears on the Southwire 4 in octagon box and 2-3/4 in between the screws of the RACO 3-1/2 in round cover and Steel City 4 in cover. - A fixture strap's own slot length and the ears of a 3-1/2 in box are not printed as numbers on the sheets found, so only the spacings above are given. Some Hubbell sheets print depth and width values that disagree with the title (the 4 in octagon RACO 175 shows 2.633 in for a 2-1/8 in box): those are left out. - The octagon file is 4 in across flats (the sheet prints width 4 in and height 4 in) with both hole pairs; the round cover file is the printed 3.500 in diameter and 0.119 in thickness. The #8-32 hole size is the thread major diameter, 0.164 in: the Hubbell sheet prints no thread, the Steel City ring pages print 8-32. - Both files are templates for designing a fixture adapter or canopy: no knockouts, ears, bosses or radii (not printed). parameter value 4 in octagon, drawn, 1-1/2 in deep (RACO 125) 15.5 cu in; 4 x 4 in; actual depth 1.563 in 4 in octagon, 2-1/8 in deep, fixture ears (Southwire 54171-DEOW) 20.0 cu in; fixture ears 3-1/2 in o.c. 3-1/2 in octagon, drawn, 1-1/2 in deep (RACO 112) 11.8 cu in; 3.500 x 3.500 in; depth 1.563 in 3-1/2 in round old work ceiling box, 2 in deep (Allied 9338-EK) 14.0 cu in; 3-1/2 in diameter; tapped device holes 3-1/2 in round cover (RACO 703) 3.500 in diameter, 0.119 in thick; screw centres 2-3/4 in 4 in octagon/round cover, 5/8 in raised (Steel City 54C3) tapped ears on 2-3/4 in centres 4 in octagon ring, 1/4 in raised (Steel City 501-CS) ears 8-32 on 2-23/32 in centres fixture screws, 3-1/2 and 4 in round and octagon 3-1/2 in o.c. (box ears) and 2-3/4 in (cover ears) ear positions on 3-1/2 in boxes, wall thickness, radii not printed: not modelled Files elsewhere (not hosted by Xem Studio; license as stated by the publisher): - Hubbell RACO: 125 4 in octagon box, drawn, 1-1/2 in deep (spec sheet) — web — Publisher's page; dimensions are facts — https://hubbellcdn.com/specsheet/RACO-125-SPEC-EN.pdf - Hubbell RACO: 112 3-1/2 in octagon box, drawn, 1-1/2 in deep (spec sheet) — web — Publisher's page; dimensions are facts — https://hubbellcdn.com/specsheet/112.pdf - Hubbell RACO: 703 3-1/2 in round cover, screw centres 2-3/4 in (spec sheet) — web — Publisher's page; dimensions are facts — https://hubbellcdn.com/specsheet/703.pdf - Southwire: 54171-DEOW 4 in octagon box, 2-1/8 in deep, fixture ears 3-1/2 in o.c. — web — Publisher's page; dimensions are facts — https://www.southwire.com/electrical-components/steel-boxes-covers-accessories/4-octagon-box-2-1-8-deep-drawn-w-conduit-ko-s-and-fixture-ears3-1-2-o-c-/p/54171-DEOW - Platt Electric (Allied Moulded data): 9338-EK 3-1/2 in round old work ceiling box (14 cu in, 2 in deep) — web — Publisher's page; dimensions are facts — https://www.platt.com/p/0576945/allied-moulded/3-1-2-round-ceiling-fixture-box-depth-2-old-work-non-metallic/085339460015/all9338ek - ABB (Steel City): 54C3 4 in octagon/round cover, 5/8 in raised, tapped ears on 2-3/4 in centres — web — Publisher's page; dimensions are facts — https://empower.abb.com/ecatalog/ec/EN_CA/p/54C3 - ABB (Steel City): 501-CS 4 in octagon ring, ears 8-32 on 2-23/32 in — web — Publisher's page; dimensions are facts — https://empower.abb.com/ecatalog/ec/EN_CA/p/501-CS Free files (CC BY 4.0, Xem Studio; STEP + STL, 2 parts): https://xemstudio.com/files/hardware/ceiling-boxes-us/index.json API: https://xemstudio.com/api/geometry?object=ceiling-boxes-us