To quote from the instructions included with this item, "The 'new' Mercury Jiffy Mask is precision die cut to provide sharp, clean edges for the projection of your single frame transparencies.  It can be used in any standard 2x2 slide projector or viewer.  For further protection of the transparency from scratches, dirt and dust, the masks can be bound between glass..."  The wording on the box says that 50 masks were enclosed.  I haven't counted, but the box appears to be full.  SELLER NOTES:   (a) I would appreciate your EXAMINATION OF PHOTOS AND DESCRIPTIONS in this ad, and raising any questions before you bid.  (b) Please note that I AM NOT AN EXPERT on any items being sold.  (c) COMBINED SHIPPING DISCOUNTS may be available as long as shipping parameters can be maximized.  With First Class shipping, that is no more than 16 ounces total weight (including box) and no more than 12 inches in any direction of the package.  With larger or heavier packages, items must fit into an available box without risk to any delicate items.  If there is any doubt about staying within these limitations, please inquire in advance.  Ideally, items for a combined shipment are purchased from one shopping cart or, if not possible, at least in quick succession.   (d) The seller purchases virtually all boxes used, in addition to the cost of other materials.  These costs become part of the “shipping and handling” paid by the buyer.