Chris King Inset I4 49mm Headset

Chris King designed the first sealed bearing headset in 1976. Thirty-four years later, the King headset remains a benchmark for quality. No other bicycle component can claim the precision, performance and absolute reliability of a Chris King headset. At Chris King Precision Components, they manufacture each headset in their own facility to exacting standards, using quality-at-the-source methods to minimize waste. Even the sealed, cartridge style bearings are made in-house and are hand-checked.
InSet™ is the classic, unbeatable Chris King sealed bearing headset built into six configurations for contemporary bicycle headtube dimensions. As a low-stack style headset, the press-in cups and bearings are housed within the headtube allowing for an overall lower ride height. The InSet also features Chris King’s GripLock™ bearing cap design that uses a multi-piece bearing cap and a split ring for improved steerer tube interface.
For help with installation and troubleshooting, Chris King has lots of info available here.