Part family

Spacers and standoffs

Standoffs, spacers, shims and washers from a plain-English description, with the stack height, the outside profile and the bore measured before you print.

What to specify

  • The stack height — how far apart the two things end up. On a standoff this is the whole point of the part.
  • The bore, and whether it is clearance or a thread. M3 clearance is 3.4 mm; 3.0 mm is the bolt, not the hole.
  • The outside profile and its size: round by diameter, hex by ACROSS FLATS, square by side.
  • Whether the hole goes all the way through or is blind, and from which end.
  • Whether the ends are flat, chamfered, or have a spigot that locates in a board hole.
  • The material you mean to print it in, if the wall is going to be thin — this is the family where it usually is.

Prompts that work

An M3 standoff 15mm tall, hex outside 5.5mm across flats, through hole for an M3 bolt.

A round spacer 8mm outside diameter, 4.2mm bore, 6.5mm long, for an M4 bolt.

A shim 20 x 20 x 1.2mm with a 5.5mm hole in the middle and two 3.2mm holes 14mm apart.

Measured examples

A standoff is the simplest part on this site and the one with the least room in it. The height is the specification, the bore is fixed by the bolt, and everything that is left over is wall — usually about a millimetre of it.

Say across flats, and expect across corners back

A hexagon has two widths. Across the flats is what a spanner reads and what a catalogue lists; across the corners is 15.5% larger, and it is what a bounding box reads, because a bounding box does not know what a hexagon is. A 5.5 mm hex standoff measures 6.35 mm corner to corner, and a report that says 5.5 expected against 6.35 measured is describing one hexagon, not a part that came out too big. Say "5.5 mm across flats" in the prompt and the ambiguity never arises.

Clearance, not bolt size

"M3" is the bolt. The hole the bolt goes through is 3.2 mm close or 3.4 mm normal clearance, and a hole actually printed at 3.0 mm is a hole you will be drilling out. If you want the bolt to thread into the part, say so — and expect it to be a worse idea than it sounds in plastic at this scale, where a printed thread strips long before the bolt does.

The wall is what is left over

Between a Ø3.4 bore and a 5.5 mm hex there is 1.05 mm of material at the flats, and that is not a choice anyone made — it is subtraction. It is also near the floor of what prints as a solid wall rather than two skins with a gap down the middle. If the stack is carrying any load, print this family with enough perimeters to fill the wall, in something stiff, or buy the brass one.

What gets measured

The bounding box, the bore diameter and count, the volume, and the thinnest span the print-readiness sampler can find. What is not measured is whether the standoff will take the torque you put through the bolt: a dimensionally perfect standoff in soft plastic still crushes.