These are a set of three three Rubber Suction Cup Feet from Manfrotto that also feature a retractable stainless steel spike. The suction cup increases the footprint of the legs by almost 20 times, giving much greater stability when needed. The steel tip provides a firmer footing on soft ground.
The foot can be removed and replaced at will.
Note: Only compatible with older versions of the 3001N, 3001BN, 3001D, 3001BD, 3001PRO, 3001BPRO, 3205GN3, 3001BWN, 756B, which feature a 19mm lower leg section. Older models show an engraved 4-digit serial number, as opposed to the longer anti-counterfeiting label used with current models.