Quarks are fermionic particles of spin ("S" = ). Because spin projections vary in increments of 1 (that is 1 ħ), a single quark has a spin vector of length , and has two spin projections ("S"z = + and "S"z = −). Two quarks can have their spins aligned, in which case the two spin vectors add to make a vector of length "S" = 1 and three spin projections ("S"z = +1, "S"z = 0, and "S"z = −1). If two quarks have unaligned spins, the spin vectors add up to make a vector of length "S" = 0 and has only one spin projection ("S"z = 0), etc. Since baryons are made of three quarks, their spin vectors can add to make a vector of length "S" = , which has four spin projections ("S"z = +, "S"z = +, "S"z = −, and "S"z = −), or a vector of length "S" =  with two spin projections ("S"z = +, and "S"z = −).