Made of perforated steel plate with square holes. Available in following aperture of 125, 160, 100, 90, 80, 75, 63, 53, 50, 45, 40, 37.5, 31.5, 26.5, 25, 22.4, 19, 16, 13.2, 12.2, 11.2, 10.2, 10, 9, 5, 8, 6.7, 6.3, 5.6, 4.75, 2.8 m.m.

(A) With brass frame 8'' dia
(B) With G.I. frame 12'' dia
(C) With G.I. frame 18'' dia