Rectangular Softboxes are widely used in Fashion & Product Photography as the Speed ring means that you can rotate the box to adjust the shape of light. Some Rectangular Softboxes are used in the Interfit Stellar Halogen range of kits. Maximum Light loss=1 stop with both baffles inserted. except RSBR8511 or above which are 1.2 stops. To fit a softbox to a head you will need to know the fitting type. If it is an intermit head it is likely to be the ASA1000 ring (S Type Fitting).