The Manfrotto 204SPK3 Retractable Spiked Feet (Set of 3) fits their "D20.4" carbon fiber 20.4mm outer diameter tube found on the 055XPROB, 055CX3 and 055CXPRO3 tripods.
The spikes are made from an anodized aluminum alloy, so they're extremely resistant to corrosion. Having spiked feet is beneficial anytime you're shooting on soft earth surfaces.
A dedicated mounting tool is included.
Specifications : Weight = 6.7 oz (190g)