Serinity sew on crystals Square (3240) in Jet UNFOILED are loose flat backed crystals that come with a thread hole, enabling the crystals to be sewn onto fabric. Serinity Square shaped crystals are a type of crystal that features a four-sided square shape with a flat top and simple bevelled edges. The shape's faceting is specifically designed to reflect and refract light, with the slight bevel adding a touch of softness to the overall appearance.