PRIMO (0 parts)
PRIMO was one of several short-lived LEGO building products aimed at very young children.
The large hemispherical studs were even easier to stack than DUPLO or QUATRO, but the system failed to gain widespread appeal and was retired in 2005.
The bricks are 6-times the size of a LEGO brick, but are only 'compatible' with other LEGO products when using the 1×1 Primo Brick w/ 4-DUPLO Studs (part 5022).