Coemar CF 1200 Hard Edge Instruction Manual page 32

B) replacing a glass gobo with a metal gobo
Metal gobos should have an external 50mm Ø with an image area of 38mm Ø;
coemar can supply a wide range of replacement gobos.
1) To insert the metal gobo, procede as per the previous instructions for glass gobos.
You will, however, require a separate retaining ring with a thickness of 1,8 mm,
similar to that shown below, which is fitted above the metal gobo directly under
the 3 retaining clips.