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Cut-off shorts/Jeans to cut-off
Invisible marking pen, chalk, washable marker
Lighter, pliers, etc.
Use the ruler and decide how close together you want the studs. Use your marking utensil to mark out a grid for the studs. I put purple dots where I am going to poke the studs just so you can see it better.
To close the studs I typically use the end of the lighter. It’s hard and small enough to poke the prong down. Some people just use their fingers and I have heard of others using pliers.
If your shorts have not already been washed and frayed be sure to leave enough room next the cut edge to allow for fraying once they’ve been washed.