Tumble Forms Replacement Lap Belt. The pelvic belt is available in four different sizes including: Small (32”), Medium (40”), Large (44”) and Extra Large (56”). The Small replacement strap is ideal for the Small Feeder Seat and Deluxe Floor Sitter. The Medium replacement strap fits the Medium Feeder Seat and Deluxe Floor Sitter. The Large replacement strap is used for the Large Feeder Seat, Large Deluxe Floor Sitter, and Universal Corner Chair. The Extra Large replacement strap fits the Extra Large Feeder Seat and Deluxe Floor Sitter.