66 blocks and 110 blocks have become “standard” names, and the origin of the name hasn’t been well documented. I’ve read that the number of the blocks comes from AT&T Labs, but I’ve yet to find any documentation.

Although 66 blocks have traditionally been considered CAT3 and lower and 110 blocks to be CAT3 and higher, you can easily find 66 blocks that work with cat5e. If you look around at the options, you’ll find the wiring industry has options for almost anyone.

At first I thought this might be the number of connections but Wikipedia says that a 66 block has 50 rows by 4 columns.

Also, it says that 110 blocks have largely replaced 66 blocks because most 66 blocks are not rated for the CAT5 standard. What about CAT6 (and up)?

Could you please elaborate more on the CAT rating for these blocks?

Thanks