Do you use Lightburn?
If you have trouble fitting items because they are too tight or too loose. 
The problem here is setting the laser in the program you use to cut. There is a parameter KERF OFFSET for shifting the laser beam by a given value. Your laser is either cutting below or above the specified value. 
Why this happens? It depends on the step setting of the stepper motors and the tension of the drive belts. It also depends on the thickness of the laser beam and the thickness of the material, whether it is 3 mm or more or less.You need to test what parameter you will need: 0.00 or e.g. 0.001
The file for testing Kerf is here: Download
And if your material is 1/8 inch (3.175 mm) and the project is for 3 mm, then enlarge this project by 105.84% and you will have it for material 1/8 inch (3.175 mm)
