Squares that play well together
The following are sizes that are compatible in piecing:
2, 3 1/2, 5, 6 1/2, 9 1/2
Two 2's make a 3 1/2, three make a 5; two 3 1/2's make a 6 1/2, three make a 9 1/2; two 5's make a 9 1/2.
OR
2 1/2, 4 1/2, 6 1/2, 8 1/2, . . . (Combinations are more obvious.)
OR
3, 5 1/2, 8, 10 1/2
Two 3's make a 5 1/2, three make an 8, four make a 10 1/2; two 5 1/2's make a 10 1/2; a 5 1/2 plus a pair of 3's makes an 8 in one direction only.