Darkroom & Studio Photographic Equipment
Broncolor Strip Mask 7.5 cm 3 for Softbox 30 x 120 1 x 3.9 ft
A 7.5cm (3in) Strip Mask for the 30x 120cm Softbox, allowing for a narrower strip of light.
https://www.bizrate.co.uk/photography_darkroomequipment/broncolor-strip-mask-7-5-cm-oid24206328159.html