Adjustable Ring Size Inlet – Parametric Model (Ring Size Reducer)

This parametric wedding ring insert allows you to resize a loose ring to match your finger diameter.

The model 3MF is included mainly for preview purposes. Measure your ring and play with the inner diameter!

The main file is provided in FreeCAD format (.FCStd) and is fully parametric.

FreeCAD is free and open-source software, available for Windows, Linux, and macOS — no subscription, no registration, no hidden restrictions.

To customize the model:

1. Open the file in FreeCAD

2. Edit the values in the included parameter spreadsheet

3. Recompute the model

4. Export to STEP, 3MF, or STL

Recommended export formats:

• STEP – best accuracy and precision (recommended)

• 3MF – good balance between quality and slicer compatibility

• STL – last resort only

Please note that STL uses a mesh approximation, so geometric accuracy is lower than that of STEP or 3MF.
For best fitting results, STEP export is strongly recommended.

You may need to experiment with your slicer wall generation settings to achieve the best surface quality and fit.

This model can be printed in either Spiral Vase mode or normal mode.

• When printing in Spiral Vase mode, you get a clean, seamless surface.

• When printing in normal mode, make sure your printer is well calibrated:

  • Proper extrusion flow

  • Correct pressure advance / linear advance

  • Seam gap set close to 0% (recommended)

  • Try the scarf joint seam

Otherwise, visible seams or small gaps may appear.

For the best surface quality and fit, it is strongly recommended to print on a smooth build plate.

• Use a small layer height, I used 0.1 mm.

• Do not use a brim.

• With reasonable dimensions, no supports are required.

• Print the model in a flat (lying) orientation as provided in the file.

• Avoid unnecessary adhesion helpers unless your material strictly requires them.

A clean bottom surface is important for proper contact with the ring and overall comfort.

For better comfort and durability, flexible materials (TPU) or PETG are recommended, but PLA also may work (I didn't test PLA).

Parameters

• InnerDiameter
  Carefully measure the inner diameter of the ring with a caliper. Accurate measurement gives the best fit on a properly calibrated printer.

• RingWidth
  Width of the ring band.

• EdgeLip
  Small retaining lip that holds the insert in place. Do not make it too large or too small — it should secure the insert without affecting the ring's appearance.

• InsertThickness
  Wall thickness of the insert. Keep in mind that actual thickness depends on your nozzle diameter and extrusion width.