This page details our recommended tolerances for metric nuts and bolts when designing for different types of manufacturing, in particular FDM 3D printing and laser cutting.

The nominal values on the page are taken from the standards for metric sized screws and nuts. If you are unsure that your screws and nuts match the standard sizes, or you already know they're non-standard or imperial sizes, then please measure them and adjust your designed tolerances before committing to manufacture.

FDM

All these values were obtained by experimentation on our Stratasys F170 3D printers using ASA print material. These values may differ for different printers and different materials, but are a good starting point.

As the X and Y axes have much more granularity than the fixed layer height of the Z axis, the tolerances required differ depending on the orientation of the hole. These values are a compromise that should work for both, but may result in slightly looser or tighter tolerances depending on orientation.

Bolt Holes

For a hole to put a bolt through a printed model:

Metric Size	Nominal bolt diameter	Recommended bolt hole diameter

Metric Size	Nominal bolt diameter	Recommended bolt hole diameter
M2	2mm	2.4mm
M2.5	2.5mm	2.8mm
M3	3mm	3.3mm
M4	4mm	4.3mm
M5	5mm	5.3mm
M6	6mm	6.3mm

 

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Nut Recess

For embedding a nut flat within a face of the printed model:

Metric Size	Nominal nut thickness	Nominal nut flat-to-flat size	Recommended recess flat-to-flat size

Metric Size	Nominal nut thickness	Nominal nut flat-to-flat size	Recommended recess flat-to-flat size
M2	1.6mm	4mm	4.4mm
M2.5	2mm	5mm	5.3mm
M3	2.4mm	5.5mm	5.8mm
M4	3.2mm	7mm	7.3mm
M5	4mm	8mm	8.3mm
M6	5mm	10mm	10.3mm

Adjust depth of recess according to needs. For a flush fit, use nominal nut thickness for recess depth.

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Nut Slot

For embedding a nut within a printed model, using a side opening slot:

Metric Size	Nominal flat-to-flat	Nominal nut thickness	Recommended slot flat-to-flat	Recommended slot thickness

Metric Size	Nominal flat-to-flat	Nominal nut thickness	Recommended slot flat-to-flat	Recommended slot thickness
M2	4mm	1.6mm	4.5mm	2mm
M2.5	5mm	2mm	5.4mm	2.3mm
M3	5.5mm	2.4mm	5.9mm	2.6mm
M4	7mm	3.2mm	7.4mm	3.3mm
M5	8mm	4mm	8.3mm	4.2mm
M6	10mm	5mm	10.3mm	5.1mm

 

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Screw Head Counterbore

For embedding a screw head flush with the face of the model:

Pan Head:

Metric Size	Nominal head diameter	Nominal head thickness	Recommended hole diameter	Recommended hole depth

Metric Size	Nominal head diameter	Nominal head thickness	Recommended hole diameter	Recommended hole depth
M2	4mm	1.6mm	4.2mm	1.6mm
M2.5	5mm	2.1mm	5.2mm	2.1mm
M3	6mm	2.5mm	6.2mm	2.5mm
M4	8mm	3.1mm	8.2mm	3.1mm
M5	9.5mm	3.7mm	9.7mm	3.7mm
M6	12mm	4.6mm	12.2mm	4.6mm

Socket Cap:

Metric Size	Nominal head diameter	Nominal head thickness	Recommended hole diameter	Recommended hole depth

Metric Size	Nominal head diameter	Nominal head thickness	Recommended hole diameter	Recommended hole depth
M2	3.8mm	2mm	4mm	2mm
M2.5	4.5mm	2.5mm	4.7mm	2.5mm
M3	5.5mm	3mm	5.7mm	3mm
M4	7mm	4mm	7.2mm	4mm
M5	8.5mm	5mm	8.7mm	5mm
M6	10mm	6mm	10.2mm	6mm

 

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Laser Cutting

Due to the kerf of the laser, cuts will end up as 0.1mm bigger then how they are specified. This means that often times you can specify the hole as the nominal size, and the kerf of the laser will make it large enough to be tolerant. These values have been determined using 3mm acrylic, values may differ for different materials.

Bolt Holes

For a hole to put a bolt through a piece of acrylic:

Metric Size	Nominal bolt diameter/Recommended hole size

Metric Size	Nominal bolt diameter/Recommended hole size
M2	2mm
M2.5	2.5mm
M3	3mm
M4	4mm
M5	5mm
M6	6mm

 

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Nut Recess

For embedding a nut part-way into a piece of acrylic to hold it in place:

Metric Size	Nominal flat-to-flat	Recommended flat-to-flat

Metric Size	Nominal flat-to-flat	Recommended flat-to-flat
M2	4mm	4.2mm
M2.5	5mm	5.2mm
M3	5.5mm	5.7mm
M4	7mm	7.2mm
M5	8mm	8.2mm
M6	10mm	10.2mm

Depth of the holder will be specified by etch power at the laser cutter.

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T-Slot

For attaching two pieces of acrylic together, perpendicularly:

 

Metric Size	Nominal bolt diameter	Nominal flat-to-flat	Nominal nut thickness	a - Slot length	b - Slot width	c - Nut slot thickness	d - Nut slot width	e - Nut slot offset

Metric Size	Nominal bolt diameter	Nominal flat-to-flat	Nominal nut thickness	a - Slot length	b - Slot width	c - Nut slot thickness	d - Nut slot width	e - Nut slot offset
M2	2mm	4mm	1.6mm	Nominal bolt length + 1 - Material Thickness	2mm	1.6mm	4mm	3mm
M2.5	2.5mm	5mm	2mm		2.5mm	2mm	5mm
M3	3mm	5.5mm	2.4mm		3mm	2.4mm	5.5mm
M4	4mm	7mm	3.2mm		4mm	3.2mm	7mm
M5	5mm	8mm	4mm		5mm	4mm	8mm
M6	6mm	10mm	5mm		6mm	5mm	10mm

 

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