Need to measure the radius of something to CAD a holder or accessory?
Need a way to model and reproduce that sleek round surface?
This might help.

Attach to a Digital Dial indicator in order to calculate the radius of a curved surface.

Designed to fit a Digital Dial Indicator with a shaft diameter of 8mm, such as
"Neoteck DTI Digital Dial Indicator 1''/25.4mm | Digital Probe Indicator Dial Test Gauge High Resolution: 0.0005''/0.01mm" on Amazon US.

How to zero:
raise/lower the plastic component along the shaft while placed on a flat surface... It should be just touching the surface at probe's full extension. Can be optionally secured using a #6 set/machine screw. There is an optional second channel parallel to the main one, in which a #6 set screw can be inserted in order to assist in holding the part off the dial indicator at a certain distance in order to help zero with more precision.

Formula for determine radius:
Radius=[(Cord Length^2) /4+ (Measured height^2)] / (2* measured height)

Chord length between long arms is 50mm
Chord length between short arms is 20mm.

Vertical offset between long and short arms is 15mm... So basically just subtract 15 from your reading if using short arms.

Excel to be included with formulas for calculation.
If using excel file is untrusted, use calculator online ( https://planetcalc.com/1421/ )

Note that, measurement (and calculated radius) accuracy decreases with increasing size of radius.

MakerGear

MakerGear M2

Doesn't Matter

Yes

0.3mm

whatever

Added Tolerance is 0.2mm for holes.rnrnPrint with arms pointed up.rnSupport is not needed if not planning on using set screw to hold, or if you don't mind 3mm holes printed perpendicular to Z axis.