Printing above a pocket

I cut a square out of quarter inch, "or simular", plywood with a smooth surface. Then with platen adhesive, stick it down on the platen. Then align the print just above the lower edge of the plywood.
Now you have a feel spot each time you put a shirt on the platen and you can line the top of the pocket down under the lower edge of the plywood.
The plywood also keeps the screen raised above the hem of the pocket so it stays out of the way.

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I do the same thing (as Greg does) but use trophy metal instead of wood. It's smoother, seems to hold the tack longer, and isn't affected by heat when flashing.

Use Laminated wood. It's at Home Depot, real cheap, Nice and smooth, and doesn't get ruined with flashing. Make a square a little bigger than your print (make sure it'll work with your clamping mech on the printer), and line the screenprint up so that when you load the shirt, the pocket will be at the edge of the platen you cut, so it'll always be in the same place.

you could just use platten rubber