The U4T Boba switch is a medium tactile switch with a D-bump with no pretravel on the downstroke, a solid bottom-out, and a nice pop on the upstroke. The stroke all the way through is smooth, thanks to the housing and stem material composition, and has a thocky bottom-out that has become very sought after. Gazzew has also gone to the effort of designing a new leaf to not only be linear and tactile friendly, but also to reduce leaf ping. The use of high-quality Korean stainless steel springs helps prevent spring ping as well.
U4 is short for Euphoria.
The "T" in U4T stands for "extra Thocccc".
Fairly loud switch with an emphasis on the "Thock".
Donut-dipped springs, light lube on leaf