Start with the weight of your screen without its stand, from the maker's specification sheet. For one or two everyday screens of up to 9 kg, the Vader (1 to 9 kg, black or white) and the Glider (3 to 9 kg, Noir Black with white trim) are gas spring arms you adjust with one hand. For screens from 24 to 57 inches, up to 27 kg flat or 22 kg curved per arm, the 2:22 Curve is the heavy-duty arm. For three or four screens on one post, the C.ME is a post system; Thinking Works states its capacity as 8 kg per arm.
Then check the desk: the C.ME fittings suit worktops 18 to 33 mm thick, the Glider clamp 10 to 60 mm, the 2:22 Curve clamp 10 to 45 mm and the Vader clamp 10 to 85 mm. Our desk compatibility checklist covers the rest, and our guide to Thinking Works monitor arms compares them in more detail.