Twin/Full size is usually applied to adjustable metal bed frames. The standard size of the twin mattress is 39" x 75" and the standard size for a full mattress is 54" x 75". Therefore, adjustable metal bed frames can be used for a twin mattress and also can be expanded to accommodate a full size as well.
Queen/King size is also usually applied to adjustable metal bed frames. The standard size for a queen mattress is 60" x 80" and the standard size for a king size mattress is 76" x 80". Once again, in this case, the adjustable metal bed frame can be used for a queen mattress and can be expanded to accommodate a king size mattress as well.