Headset Size Calculator — Find Your Headset Type

Headset Standards

• EC (External Cup): Traditional cups sit on top of the head tube
• ZS (Zero Stack): Cups press into the head tube, flush with the surface
• IS (Integrated): No cups, bearings sit directly in frame bore
• Numbers (e.g., ZS44/ZS56) indicate the head-tube BORE (ZS/EC) or bearing SEAT (IS) in mm — not the bearing OD
• The cartridge bearing OD is smaller than the seat/bore number: EC34/ZS44 → 41.8 mm bearing; IS41 → 41.0 mm bearing (41.1 mm seat); IS42 → 41.8 mm bearing (~42 mm seat); ZS56/IS52 → 52 mm bearing (~52 mm seat)
• Integrated (IS) bearings drop straight into machined seats — an integrated tapered frame is typically IS42/IS52 (41.8 mm upper, 52 mm lower); the less-common IS41/IS52 uses a 41.0 mm upper
• Tapered: upper bearing (41.0–41.8 mm) is smaller than lower (52 mm), to suit a steerer flaring from 1⅛" (28.6 mm) to 1½" (38.1 mm)