Summary

18 mm/22 mm diameter aluminium shaft, the thread pitch is 1 mm

It is similar to the part E in the following diagram:
https://www.barskasupport.com/spare-part-order/lock-nut-assembly

You could complement it with https://www.thingiverse.com/thing:3541435

It is originally for https://www.jula.no/catalog/fritid/fritidsaktiviteter/metalldetektorer-og-kompasser/metalldetektorer/metalldetektor-150058/ Marquant Metal Detector but it seems similar to the Barska Master edition metal detector.

Print Settings

Rafts: 

Doesn't Matter

Supports:                     

No

Resolution: 

0.2 to 0.1 variable (for the threads is best)

Infill:                     

50%
 

Notes: 
 

Rotate the shape and print with the threads pointing up. No supports required. No cleanup