Two values in one variable

Let's say you have two small values that will never get past 10, and you use the first four bits of a char for the first var and the last bits for the second var. Do people do that?

#define GET_BIT(var,n) (var &= 1<<n)
#define SET_BIT(var,n) (var |= 1<<n)
#define CLEAR_BIT(var,n) (var &= ~(1<<n))