Chicago screws (binding posts, barrel bolts, sex bolts): barrel and head diameter, thread, hole size and lengths, 8-32 / 10-24 / 1/4-20 — dimension sheet Source: Xem Studio, https://xemstudio.com/objects/chicago-screws-binding-posts/ (sheet CC BY 4.0) Basis: Rivets Online (steel, three thread sizes), screwpost.com (aluminum 8-32) and McMaster-Carr's low-profile 8-32 table, as printed; maker / distributor numbers only, there is no standard behind these Catalog version: 2026-10-20 Sizes: see table below - There is no ASME or ISO standard for Chicago screws (also sold as binding posts, binder posts, barrel bolts, sex bolts or screw posts); each maker sets its own sizes and the makers below do not agree on head diameter. Check the part you buy. - Rivets Online (steel): 8-32 barrel .203, head .415, hole 7/32; 10-24 barrel .250, head .438, hole 17/64; 1/4-20 barrel .312, head .562, hole 21/64. The page prints an 8-32 hole of '17/32 (.218)', which is a typo for 7/32 (.218) as its filter list says. The page's filter also lists a '10-24 with .262 body diameter' and does not say which of .250 and .262 belongs to which product. - screwpost.com (aluminum): 3/16 post, 8-32, 7/16 head on both post and screw, 'fits in a 1/4 inch hole'. McMaster-Carr (aluminum, low profile): barrel 13/64, head 13/32 x 1/16, screw head 13/32 x 1/16. For 8-32 the three makers give heads of 0.415, 0.4375 and 0.406 in and barrels of 0.203, 0.1875 and 0.203 in. - Lengths are barrel (post) lengths under the head, matched to the material thickness (grip) the barrel clamps; the screw is shorter than the post. The McMaster table rows are for 1/8 to 1 in material in 7 steps. - No file: the thread depth, the head profile (flat / dome) and the screw tip are not given as numbers in the sources read, so a model would be invented. McMaster-Carr sells binding barrels and screws with per-part STEP; linked, not copied. source thread barrel dia (in) head dia (in) hole (in) barrel (post) lengths (in) screw lengths (in) note Rivets Online, steel 8-32 .203 .415 7/32 (.218) 3/16, 1/4, 3/8, 1/2, 5/8, 3/4, 1, 1-1/4, 1-1/2, 1-3/4, 2 1/4, 3/8 page also prints a 17/32 hole for this row; .218 and the filter list 7/32 Rivets Online, steel 10-24 .250 (page filter also lists a .262 body) .438 17/64 (.265) 1/4, 3/8, 1/2, 5/8, 3/4, 1, 1-1/4, 1-1/2, 2 5/16 extension: 10-24, 1/2 long, 1/4 diameter, 17/64 hole Rivets Online, steel 1/4-20 .312 .562 21/64 (.328) 3/8, 1/2, 5/8, 3/4, 1, 1-1/4, 1-1/2, 2 5/16 screwpost.com, aluminum 8-32 3/16 (0.1875) 7/16 (0.4375) fits a 1/4 hole sizes by material thickness 1/8 to 6 in; posts 3/8 and under are tapped through — head dia is the same on post and screw; extensions 1/4, 1/2, 3/4, 1 McMaster-Carr low-profile, 6063 aluminum, slotted 8-32 13/64 13/32 (barrel head, 1/16 high; screw head 13/32 x 1/16) not listed barrel 1/8 (for material 1/8 to 3/16) screw 3/16 thread depth 3/16 McMaster-Carr low-profile, 6063 aluminum, slotted 8-32 13/64 13/32 (barrel head, 1/16 high; screw head 13/32 x 1/16) not listed barrel 3/16 (for material 3/16 to 1/4) screw 1/4 thread depth 1/4 McMaster-Carr low-profile, 6063 aluminum, slotted 8-32 13/64 13/32 (barrel head, 1/16 high; screw head 13/32 x 1/16) not listed barrel 1/4 (for material 1/4 to 3/8) screw 1/4 thread depth 1/4 McMaster-Carr low-profile, 6063 aluminum, slotted 8-32 13/64 13/32 (barrel head, 1/16 high; screw head 13/32 x 1/16) not listed barrel 3/8 (for material 3/8 to 5/8) screw 3/8 thread depth 3/8 McMaster-Carr low-profile, 6063 aluminum, slotted 8-32 13/64 13/32 (barrel head, 1/16 high; screw head 13/32 x 1/16) not listed barrel 1/2 (for material 1/2 to 3/4) screw 3/8 thread depth 3/8 McMaster-Carr low-profile, 6063 aluminum, slotted 8-32 13/64 13/32 (barrel head, 1/16 high; screw head 13/32 x 1/16) not listed barrel 5/8 (for material 5/8 to 7/8) screw 3/8 thread depth 3/8 McMaster-Carr low-profile, 6063 aluminum, slotted 8-32 13/64 13/32 (barrel head, 1/16 high; screw head 13/32 x 1/16) not listed barrel 3/4 (for material 3/4 to 1) screw 3/8 thread depth 3/8 Files elsewhere (not hosted by Xem Studio; license as stated by the publisher): - Rivets Online: Binder post and screws (Chicago screws), steel: barrel diameter, head diameter, thread, hole size, post and screw lengths for 8-32, 10-24 and 1/4-20 — web — Maker/distributor page; numbers only — https://www.rivetsonline.com/binder-post-barrel-nuts-chicago-screws/steel-post-and-screws-chicago-screws-barrel-nuts - screwpost.com: Aluminum screw posts (Chicago screws): 3/16 post, 8-32, 7/16 head, 1/4 hole; sizes by material thickness — web — Maker/distributor page; numbers only — https://www.screwpost.com/index.php?cPath=1 - McMaster-Carr: Aluminum low-profile binding barrels and screws, 8-32: material thickness, barrel length, barrel and screw head dimensions (page table as printed) — web — Distributor catalog page; numbers only — https://www.mcmaster.com/aluminum-binding-bolts No true-size file yet: the published figures do not fix the whole shape; a measured scan is planned. API: https://xemstudio.com/api/geometry?object=chicago-screws-binding-posts