Cáscara is the timbale player's secret weapon. Spanish for "shell," cáscara refers both to the place the rhythm is played (the metal shell, or paila, of the timbale, struck with the side of the stick) and to the pattern itself — a syncopated 8th-note figure that complements clave and contrasts with the bell. In a traditional Cuban band, the timbale player switches between bell, cáscara, and abanico (a snare-roll cue) over the course of a tune; cáscara is the verse pattern, bell is the chorus pattern.
On the drum kit, cáscara doesn't have a literal home — there's no timbale shell. So we voice it on whatever resonant metal-or-wood surface we have: the floor-tom rim (most common), the bell of the ride (when louder), or the shoulder of the closed hi-hat (the quietest option). The pattern stays the same; only the colour changes.
Cáscara in 3-2 clave direction, played as 8th notes across two bars. Hits on: 1, &-of-1, &-of-2, &-of-3, 4 / 1, 2, &-of-2, &-of-3, 4, &-of-4. Some authors notate it slightly differently — there are several common phrasings — but the rhythmic shape is consistent. The pattern has more notes than clave (cáscara is a flowing 8th-note pattern; clave is sparse), so cáscara can contain clave inside it.
For the kit drummer, cáscara is the bridge from "playing time on a hi-hat" to "playing time on a Latin instrument." Once cáscara is in the right hand, you can put clave under your left foot, the bombo on the kick, and a snare or tom comp on the left hand — that's a complete one-person Latin ensemble. It's also the verse-version of the mambo bell groove, so you can switch between bell (chorus) and cáscara (verse) in a single tune.