The Dycem 'Black Hole' rubbercello end-pin stop/mat. It is much blacker in real life than it looks in the pictures.
Dycem STN1130 "Hole" Non Slip Cello Mat - Black
Dycem non slip patches for bagpipes
Cello Anti-slip Mat, Cello Mat Portable Non Slip Cello Endpin Rest Holder with Metal Eye Instrument Accessory (Brown)
Cheerock Non-slip Cello Endpin Anchor Stopper Rest Holder Stand Anti-slip Device for Cello Adjustable Cello Endpin Strap with Thickened Foam Pad, Great for Cellist Practice Performance
Adjustable Cello Endpin Holder Antiskid Cello Pad Non-Slip Cello Mat Anti-Slip
