This 35mm Mounted Slide Strip Mask Set for up to 4 slides, fits the Omega Negative Carrier Holder D-size for use in the Omega D5500 Enlargers, and D-size mask sets up to 4 x 5".
The mask set and the carrier are part of Omega's instant change negative carrier system, which allows you to switch out negative carriers in a quicker manor saving you time in the darkroom.