What to measure
Two kinds of pipe are commonly 18 mm outside. One is metric copper tube, where 18 mm is a standard size used for heating and water runs in much of continental Europe. The other is multilayer pipe, the plastic and aluminium composite used for underfloor and radiator circuits, which is sold in sizes such as 16, 18 and 20 mm. Both are named by outside diameter, so the caliper should read close to 18.0 mm. Check anyway. Multilayer pipe comes off a coil and can be slightly oval, so measure it across two directions and use the larger figure. If the pipe wears a corrugated sleeve or foam insulation, decide whether the clip grips the pipe or the sleeve, and measure that.
Clearance, wall and material
The clearance here is 0.3 mm, for a bore of 18.3 mm, which allows for a pipe that is not perfectly round. On bare copper you can drop to 0.2 mm for a firmer hold. The wall is 2.2 mm and the opening 100 degrees, leaving a gap of about 14 mm to push the pipe through. Heating pipe gets hot, and that decides the material: PLA softens at around 60 degrees C and relaxes under steady load well before that, so a PLA clip on a flow pipe slowly opens. Use PETG or ASA for anything connected to a boiler or a manifold, and keep PLA for cold feeds and for dry jobs such as holding a tube on a workshop wall.
Printing
Print the clip standing on a C-shaped face, with the layers running around the pipe. The footprint is about 37 by 19 mm and the height 14 mm. No supports are needed. With a 0.4 mm nozzle, three perimeters fill the 2.2 mm wall almost completely and the slicer closes the remainder with gap fill; check the preview for a thin unfilled line in the middle of the arms and add a perimeter if you see one. PETG likes to leave a fine string across the opening, which is easy to pick off once the part is cool.
Fixing it
The tab is 14 mm long and 3 mm thick with a 4.2 mm hole for a 4 mm screw. Pipe that warms up grows in length, so along a straight run let the pipe slide in the clips and do not pinch it; the 0.3 mm clearance is there for that as well. Put a clip close to each side of a bend, where the pipe tries to spring back, and space the others evenly between.
Outline drawing
Schematic, not to scale. The clip is 14 mm wide along the pipe and about 19 mm high.
Parameters the generator will use
| Setting | Link parameter | Value |
|---|---|---|
| Model | model | pipe_clip |
| Pipe diameter | diameter | 18 |
| Fit clearance | fit_clearance | 0.3 |
| Clip wall thickness | wall | 2.2 |
| Clip width along the pipe | width | 14 |
| Opening angle, degrees | opening | 100 |
| Screw tab length | tab_length | 14 |
| Screw tab thickness | tab_thickness | 3 |
| Screw hole diameter | screw_diameter | 4.2 |
| Number of screw tabs | tabs | 1 |
All lengths are in millimetres. Outer size from these values: about 36.7 x 14 x 19.05 mm.
Open the generator with these values
This model needs the $7 licence key: one payment, one key, and it opens all five paid models. Get a licence key on Gumroad ($7)
The pipe and cable clip needs a licence key: without one the generator shows the model locked, lists the values from this link and fills them in as soon as you unlock. The fitted drawer organiser bin is the free model and downloads with no key.