$79.95
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 055CXPRO3/4 tripods. 204SPK3
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.