これはサイズがあいません。

this (indicating an item near the speaker, the action of the speaker, or the current topic); this person (usu. indicating someone in one's in-group); now; here; I (me); certainly

topic marker particle; indicates contrast with another option (stated or unstated); adds emphasis

size

indicates sentence subject (occasionally object); indicates possessive (esp. in literary expressions); but; however; still; and

to meet; to encounter; to see; to have an accident; to have a bad experience