Will this work?

[Mathew Blakeway]

While browsing websites on fly fishing knots and I came across a 'Quick Grays Loop' for attaching a leader to a fly line, using a 'perfection loop' on the leader and doing a 'loop to loop'. It makes it easier to attach new leaders.

My question is; how effective is this and is it reliable?

  

[Bill Purmort]

It will totally work, and the smaller the loop the better.  learn to tie them about dime size. 

[Mathew Blakeway]

How do you get them so small?

[Bill Purmort]

It is easier if you tie a short piece to the fly line with an Albright or nail knot first and then your loop on the end of that. Just work your loop down to the size you want before cinching it tight

[David, aka, "McScruff"]

As Bill says, this is the classic way to make the connection.

You can make the loop smaller if you tie it around a small dowel or stick. Its a good way to get the hang of how the knot works; eventually you can eliminate the dowel.