Sigma 100-400 / Tripod socket: Sony Alpha Full Frame E-mount Talk Forum: Digital Photography Review
SIGMA TRIPOD SOCKET TS-111 | pvmlive.com
iShoot Lens Collar Tripod Mount Ring Support Holder BracketCompatible with Sigma 105mm f/1.4 DG HSM Art (EF/FX/FE/L Mount) & Sigma 100-400mm f/5-6.3 DG DN OS (E/L Mount) Lens, Bottom is Arca Fit