This UTG Pro SD line is made for suppressors. This sku has an ID of 1.67" which makes this a "slim" suppressor compatible handguard. Many others would be much wider.
Ok so UTG Pro offers a 1.3" ID as well, but the only suppressor tucking in that tube, is a 22lr can. The SD in the product description stands for suppressor. This is for people who want to tuck the can under the handguard.