Designed for ABS-like resin. Pin it to your pocket, you can pick out and put back the chalk with the cap only using one hand and without getting messy with the chalk powder.The cap clicks into the house with small flexible hooks, that avoids falling out after some wear.Fits standard 22X22 mm chalks and 25X25 hexagonal chalks also.It loooks much better if you spray it with clear acrylic laque after curing.