Check the listing for details. Coffee Knock Box, 4 Inch Plastic Polygonal Knock Box Coffee Grounds Bin, Black. Condition: New. Listed at 16.68 USD. Descriptions:Durable Material: This coffee knock box is made of ABS plastic, making it sturdy, durable, and highly stable. The rubber ring on the bottom of the box features a non-slip, shock-absorbing design to ensure stability when tapping coffee grounds and prevent scratching the work surface during use.Practical Design: This polygonal knock box features an innovative tapping bar-less design, preventing coffee grounds from sticking, reducing residue, and making it easier to clean. The rubber-lined tapping surface provides excellent cushioning, reducing residue buildup and tapping noise. Compact size & easy to clean: This espresso knock box is compact in size, making it easy to place on a countertop. It has a large enough capacity to hold a coffee puck and prevents coffee grounds from splattering.