Originally, Jack knives had squared off bolsters. The Sleeve Board pattern rounds both end and is tapered from one end to the other. It gained its name because it was shaped like the attachment for an ironing board to iron sleeves.
Historically, sleeveboard patters have housed a number of different blades. Usually they are hinged on the larger end of the frame.
Great Eastern Cutlery, living up to their passion for traditional knives, makes a number of different versions of the sleeveboard. The #15 is 3.5" closed.