My husband has tried various other brands of socks ,none of which
remotely resembled the L/XL I chose for him.
He finds Posey socks comfortable and true to advertised sizing.

Quickie Q400 M/F/R
Length: Max. 1190 mm
Seat Width: 385 - 510 mm
Seat Height: 415 - 490 mm
Seat Depth: 410 - 560 mm
Backrest Height: 460 - 510 mm
Back Recline: 85° to 120°
Turning Radius: 735 mm
Speed: 10 kph
Batteries: 60 Ah
Maximum Safe Slope: 8°
Max Kerb Climb: 70 mm
Electronics: VR2
Min. Weight: 130 kg
Maximum User Weight: 136 kg