# Chicago screws (binding posts, barrel bolts, sex bolts): barrel and head diameter, thread, hole size and lengths, 8-32 / 10-24 / 1/4-20

> What size hole does a Chicago screw (binding post) need, and what are its barrel diameter, head diameter and lengths?

- Category: Hardware › Fasteners
- Kind: Standard part
- 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
- Page: https://xemstudio.com/objects/chicago-screws-binding-posts/ · JSON: https://xemstudio.com/api/geometry?object=chicago-screws-binding-posts · Plain text: https://xemstudio.com/objects/chicago-screws-binding-posts/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); files CC BY 4.0 or their publisher's license
- Use in every chat: add https://xemstudio.com/mcp as a connector (https://xemstudio.com/use-with-ai/)

**Exact dimensions.** True size, with no tolerance added.

## Notes

- 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.

## Sizes

| 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 |

## Where the files are

- 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](https://www.rivetsonline.com/binder-post-barrel-nuts-chicago-screws/steel-post-and-screws-chicago-screws-barrel-nuts) — web — Maker/distributor page; numbers only
- screwpost.com: [Aluminum screw posts (Chicago screws): 3/16 post, 8-32, 7/16 head, 1/4 hole; sizes by material thickness](https://www.screwpost.com/index.php?cPath=1) — web — Maker/distributor page; numbers only
- McMaster-Carr: [Aluminum low-profile binding barrels and screws, 8-32: material thickness, barrel length, barrel and screw head dimensions (page table as printed)](https://www.mcmaster.com/aluminum-binding-bolts) — web — Distributor catalog page; numbers only

## Questions

**What size hole does an 8-32 Chicago screw need?**

Rivets Online lists a 7/32 in (0.218 in) hole for its 8-32 steel binder post (barrel .203 in); screwpost.com says its 3/16 in aluminum post 'fits in a 1/4 inch hole'. McMaster-Carr does not list a hole for its 13/64 in low-profile barrel.

**What are the common Chicago screw thread sizes?**

8-32 is the common one (screwpost.com calls it the industry standard); Rivets Online also lists 10-24 and 1/4-20.

**Is a Chicago screw the same as a sex bolt?**

Both names are used for a barrel (post) that a screw threads into; sellers file them together (barrel bolts and screws, binding barrels). Sizes are per maker, with no standard.

## Fits with

- [Imperial machine screws: #4-40, #6-32, #8-32, 1/4-20](https://xemstudio.com/objects/imperial-machine-screws/)
- [Rivet nuts (blind threaded inserts), flat head: hole size, grip range, body and flange dimensions, M3–M12 and #6-32 to 3/8-16](https://xemstudio.com/objects/rivet-nuts-flat-head/)
- [Blind (pop) rivets, dome head: 3.2, 4.0, 4.8 mm and 1/8, 5/32, 3/16 in: hole size, head diameter, grip range, length](https://xemstudio.com/objects/blind-pop-rivets-dome-head/)
- [Screw-on rubber feet and threaded rubber bumpers: Essentra SOF / BF series and Ganter GN 352.1 / 352.2 (452) sizes, thread, load](https://xemstudio.com/objects/screw-on-rubber-feet-and-bumpers/)
- [Hex nuts, inch: #4-40 to 3/4-10 (ASME B18.2.2)](https://xemstudio.com/objects/hex-nuts-inch/)