mmono

Not all 20mm Are Equal

This is an over-engineered mono hangboard pickup for climbing 🥑

Dimensions

Design

What is a 20 mm edge?

For a 90° angle, it’s simple.

For a perfect 90° angle, it’s simple—the distance (shown in red) is exactly 20 mm.

But a 90° edge is harsh on the skin. Sharp edges concentrate stress at a single point, increasing pain and the chance of skin splitting. That’s why all popular hangboards have rounded edges, called fillets in CAD.

Edge Fillet: A smooth, curved surface with a constant radius that rounds off a sharp corner or transition between two intersecting faces.

Fillets are usually described by their Edge Radius — the larger the radius, the rounder the edge.

Unfortunately, there is no universal fillet radius for hangboards. Different brands use different edge radii:

Brand / Board	Edge Depth	Edge Radius	Source
Tension	10 mm	3.175 mm (≈ 1/8”)	Tension Climbing
Beastmaker	10 mm	8 mm	Test4Climbing
Lattice	10 mm	10 mm	Climbing.com

Note: Needs more data but is hard to find.

Where there is a fillet, the effective edge depth changes. What counts as “correct” depth (red lines)?

This might sound negligible, but millimeters matter for climbers.

To objectively define a true edge depth, we must agree on some definitions:

• Total Depth: The total depth, ignoring edge radius (90° diagram)
• Edge Radius: The measurement of a curved edge
• Effective Length: The usable length along its surface
• Ineffective Length: The unusable length along its surface
• Effective Depth: The usable depth of the edge

Since there’s no standard definition of Effective Length and Depth, the goal is to propose a mathematically ok-ish definition.

For a 90° angle, it’s simple. The red line is the usable edge. Your fingers hang there. The blue line is the unusable edge. Your fingers cannot hang there.

For a perfect right angle, the tangent of the corner is undefined, but if there’s a small radius (0.01 mm), the tangent gradually transitions from horizontal to vertical, with the midway point at 45°.

Based on this, we can define the Effective Length as the distance along the edge up to this midway point of the fillet.

Now that Effective Length is defined, we can calculate Effective Depth.

Use the unit circle as a reference.

Given Edge Radius & Effective Depth, calculate Total Depth:

Set edge_radius (blue) = 8mm
Set effective_depth (dotted) = 20mm

Solve for total_depth (green)

red_line = cos(45) * 8mm
pink_line = edge_radius - red_line

total_depth = effective_depth + pink_line
green = dotted + pink

A one line equation

total_depth = effective_depth + (edge_radius * (1 - cos(45))

total_depth = effective_depth + (edge_radius * (1 - 0.5 ** 0.5))

Python

import math

effective_depth = 20

edge_radius = 8

total_depth = effective_depth + (edge_radius * (1 - 0.5 ** 0.5))

print(total_depth)
# total_depth = 22.34314575050762

Finally, use calculated Total Depth to extrude your mono

Then create your Fillet Radius.

Conclusion:
A 22.343 mm deep mono + 8 mm fillet radius gives exactly 20 mm effective edge depth.