The caja china (also cajita china) is a slotted block of hardwood played with two sticks: a woodblock. The jam block is its modern hard-plastic version, now found on many timbales and drum kits.
The caja china is a rectangular block of hardwood with rounded ends. The two long sides have slots that stop short of the ends and do not go all the way through the wood, which gives the block its hollow, dry sound. According to the Cuban encyclopedia EcuRed, the instrument reached Cuba in the mid-19th century with immigrants from Manila and southern China.
In rumba the caja china can take over the pattern of the guagua. Far from every rumba group still has one: the guagua pattern is often played on the side of a tumbadora or cajón instead, alongside the catá.
In son it is rarely used. When it is, it is attached to the pailitas or sounds together with the cowbell (cencerro) in the montuno, as a contrast to the improvisation.
Songo brought a Cuban hybrid of timbales and drum kit: from timbales with a kick drum to a full drum kit augmented with timbales, a woodblock and various cowbells. In the basic pattern the right hand plays a closed hi-hat, a woodblock or a cowbell. That pattern derives from the cáscara of guaguancó, originally played on the guagua.
Most timbales have one or more cowbells and a woodblock mounted just above the drums. That is how it is part of the timbales in timba too, nowadays often as a jam block.
The jam block is a hard-plastic woodblock. Martin Cohen, founder of Latin Percussion, developed it after percussionist Marc Quiñones asked for a sturdier woodblock. Jam blocks are usually mounted on timbales and drum kits and are widely used in salsa and other Latin American styles. It lasts longer than a wooden block.