This is an embossing plate for a celtic knot.

It can be used for impressing the pattern on polimer clay or leather.

Impression profile is only 0.5mm wide and protrude only 1mm above 3mm thick base plate so it does not break under pressure when you use a clamp to press it into leather.

Several sizes are exported as different STLs (each with 0.5mm wide profile) because simply scaling it for printing will increase the width of the impression lines and specifically produce multiple lines as FDM printers will most likely use multiple shells to print them.