heat-set-inserts: SL-type heat-set inserts for OpenSCAD

Models of brass SL-type heat-set inserts (double twill knurl), M2 to M6, and cutters for the holes they go in. 114 sizes, as sold on AliExpress by the HotXYZ Official Store, with their dimensions from the seller's measurement tables. Made for checking fits and collisions in 3D-printed parts, and for drawing assemblies.

inserts.scad   the library: the size table, the insert, its hole; draws nothing by itself
preview.scad   the viewer: open it to see the inserts, their hole cutters, or the two together
inserts.csv    the same size table, with the listings each size comes from
docs/          the pictures in this README

Use

Add it to your project as a git submodule, or copy inserts.scad:

git submodule add https://git.octr.is/rbanic/heat-set-inserts.git heat-set-inserts

include <heat-set-inserts/inserts.scad>    // use <...> works too

$fa = 1; $fs = 0.05;            // the library follows your $fa / $fs (or $fn)

// a block with a blind hole for an M3 x D4.6 x L5.0 insert, and the insert set in it
difference() {
    translate([-5, -5, -10]) cube([10, 10, 10]);
    insert_hole("M3xD4.6xL5.0");
}
installed_insert("M3xD4.6xL5.0");

include also gives you the table (INSERTS) and lets you change the defaults (INSERT_HOLE_ALLOWANCE, INSERT_HOLE_CHAMFER); use keeps the library's names out of your file. The library sets no $fa, $fs or $fn of its own.

An insert is named thread x outside diameter x length, in mm: "M3xD4.6xL5.0". Every size is in the table under Sizes.

Frame

• heat_insert() stands on z = 0, the end that goes into the hole first down, its top face at z = L.
• installed_insert() and insert_hole() share one frame: the origin on the part's surface, the hole going down -Z. The insert's top face is flush with the surface. The cutter pokes 1 mm out of the surface so it cuts cleanly.

Modules

Module	Draws
heat_insert(size)	the insert, standing on z = 0
installed_insert(size)	the insert as installed: top face on z = 0, going down
insert_hole(size, depth, allowance = 0.1, screw = 0, chamfer = 0.5)	the cutter for its hole (see Holes). depth defaults to a blind hole; give more than the wall for a through hole. screw adds that much clearance hole below the bottom, for a screw longer than the hole

Functions

Function	Returns
insert_row(size)	the size's row of INSERTS, or undef
ins_size(r), ins_m(r), ins_d(r), ins_phi2(r), ins_phi3(r), ins_l(r)	name, thread, outside diameter D, Φ2, Φ3, length L
ins_segs(r)	[L2, L3, L4, L5, L6]
ins_pitch(r), ins_bore(r)	the thread's coarse pitch; its internal minor diameter (ISO 965), drawn as the bore
ins_hole_d(r, allowance), ins_hole_depth(r)	the hole's diameter and blind depth
ins_min_wall(r)	the least wall to leave round the hole
ins_clearance(r)	the ISO 273 medium clearance hole for the thread

A size that isn't in the table stops with a message naming it.

What is drawn

Going from the end that goes into the hole first to the top face:

	Section	Diameter
L2	smooth lead-in	not dimensioned; drawn at Φ2
L3	neck	Φ3, the smallest outside diameter
L4	lower knurled band	D
L5	groove between the bands	Φ2
L6	upper knurled band, to the top face	D

L2 + L3 + L4 + L5 + L6 = L on every size. Only what the seller dimensions is modelled: the knurls are plain cylinders at D (the two bands are diagonal knurls of opposite hand; their teeth aren't dimensioned), the bore is the thread's minor diameter without a thread, and there are no chamfers.

Holes

• Straight, not tapered: these are straight inserts (Spirol allows at most 1 degree included taper for them). The top sits flush.
• Diameter: Φ2 + allowance (0.1 mm). CNC Kitchen's holes are their inserts' pilot diameter + 0.1 (+0.15 for the Voron M3), and Φ2 of the SL inserts with the same outside diameter equals their pilot (3.1 at D3.6, 4.25 at D5.0). The knurls (D) melt into the wall.
• Blind depth: L + max(1 mm, 2 thread pitches): room for the plastic the insert pushes ahead of it (CNC Kitchen: about 1 mm), and so the screw can't bottom out (Spirol: 2 pitches). A through hole needs no more than L.
• Chamfer: 45 degrees at the mouth, chamfer (0.5 mm) deep, so the plastic the knurls push up has somewhere to go instead of standing proud round the insert and needing to be cut off. It also centres the insert.
• Wall: ins_min_wall() is CNC Kitchen's least wall round the hole, by outside diameter.
• Printed holes come out small, and horizontal ones sag at the top: print a test piece and adjust the allowance.

Sources: CNC Kitchen's design rules and insert table; Spirol, "How to design the proper hole for heat/ultrasonic inserts".

The viewer

Open preview.scad. By default it shows every size, one row per thread x outside diameter, shortest first.

Setting	Does
INSERT	all, or one size: its dimensions and hole go to the console
SHOW	insert, cutter (the hole), or fit (a block with the hole and the insert set in it)
CUTAWAY	cut the front half away to show the profile
ALLOWANCE, CHAMFER	the hole's diameter allowance and mouth chamfer

Sizes

Thread	D	Lengths L
M2	3.0	2.0, 2.5, 3.0, 3.6, 4.0, 4.5
M2	3.2	2.0, 2.5, 3.0, 3.6, 4.0, 4.5
M2	3.5	2.5, 3.0, 3.6, 4.0, 4.5, 5.0
M2	3.6	3.0, 3.6, 4.0, 4.5
M2	3.8	3.0, 3.6, 3.8, 4.0, 4.5, 5.0
M2	4.0	3.0, 4.0, 4.5
M2.5	3.5	2.5, 3.0, 3.6, 4.0, 4.5
M2.5	3.8	2.5, 3.0, 3.6, 4.0, 4.5
M2.5	4.0	2.5, 3.0, 3.6, 4.0, 4.5, 5.0
M2.5	4.2	2.5, 3.0, 3.6, 4.0, 4.5, 5.0
M3	4.6	3.0, 3.6, 3.8, 4.0, 4.5, 5.0, 5.5, 5.7, 6.0, 6.5, 7.0
M3	5.0	3.0, 3.6, 3.8, 4.0, 4.5, 5.5, 6.0, 6.5, 7.0
M4	6.0	5.0, 5.5, 5.7, 6.0, 6.5, 7.0, 7.5, 8.0
M4	6.5	5.0, 5.5, 5.7, 6.0, 6.5, 7.0, 7.5, 8.0
M4	7.0	5.0, 5.5, 6.0, 7.0, 8.0
M5	7.5	5.0, 6.0, 7.0, 8.0, 9.0
M5	8.0	5.0, 6.0, 7.0, 8.0, 9.0
M6	9.0	6.0, 7.0, 8.0, 9.0, 9.5
M6	9.5	6.0, 7.0, 8.0, 9.0, 9.5

inserts.csv has every dimension of every size, and the listings whose tables have it.

Sources

The dimensions are from AliExpress: the measurement tables in the descriptions of six listings by the HotXYZ Official Store, transcribed on 2026-10-16. The seller says each table is one batch measured by hand, and "there is a certain error". The listing pages and photos are the seller's and aren't in this repository.

Listing	Threads	Outside diameters	Sizes in its table
4000232526110	M2	D3.0, D3.2, D3.5, D3.6, D3.8, D4.0	31
4000378858302	M2.5	D3.5, D3.8, D4.0, D4.2	22
4000232858343	M2, M3	D4.0, D4.6, D5.0	23
4000761483243	M2, M3	D4.0, D4.6, D5.0	23
4000232925592	M4	D6.0, D6.5, D7.0	21
4000232990523	M5, M6	D7.5, D8.0, D9.0, D9.5	20

The listings sell some sizes their tables don't have, and those aren't modelled: M2xD4.0xL5.0, M3xD4.2 (every length), M3xD5.0 in L4.8, L5.0, L5.7 and L8.0, M4xD6.0xL4.0, M5xD7.0 (every length) and M5xD7.5xL4.5. The M2.5 listing sells D3.55 and D4.05, which its table calls D3.5 and D4.0; they're here under the table's names.

Checked

• inserts.csv matches the table in inserts.scad, and L2 to L6 add up to L on every size.
• Every size set in its own hole (installed_insert() against a block minus insert_hole()): nothing inside Φ2 touches the hole wall, and the knurls do.

License

Not chosen yet.