If you are going to use a Wind-On leader with your Spinning reel, one of the choices you face is how to make the loop on your mainline for the loop-to-loop connection between it and the Wind-On leader. (Loop-to-Loop photo below.) The loop-to-loop connection lets you change leaders reliably and quickly, in 6' seas, a 20 knot wind, when the temperature is 50 degrees, at night. And if you have pre-tied swivels/split rings to your spare leaders, there are no knots to be tied when the bite is on.
The mainline loop is a critical part of a loop to loop connection system. Done correctly, the mainline loop is a line-doubler. A well chosen line-doubler reduces the tension of the in the loop by half, with no loss of strength (e.g. if the mainline tension is 40 lbs., the tension in the line inside the loop, is only 20 lbs--almost magic).
Halving the tension in the loops is key to the loop-to-loop connection because the loop-to-loop knot itself is a 60-65% knot. Simple math (and real world testing and experience) says that a 60% efficient knot, running at half of the tension of the mainline, is a 120% connection. Of course 120% is meaningless but it does guarantee you a 100% strong connection--no loss of line strength in the connection. (Note: A single loop-to-loop connection is all that is needed.)
For spinning reels, the ideal mainline loop is:
--thin and without knots so that it does not catch loops of line on the spool, leading to wind-knots;
--sized small so that it can't loop around a guide during casting;
--and does not reduce the strength of the line.
Some examples of mainline loops, photos below:
1. Spliced End-Loop in hollow-weave Spectra. This is a thin, reliable way to form a line-doubler loop. There are no points of stress concentration and it is easy to make perfectly. The spliced End-Loop can be made in any loop size from fractions of an inch to feet. The catch is that you need hollow-weave Spectra.
If you prefer solid-weave Spectra as your mainline, a good alternative is to splice 5 to 10 yards of hollow-weave Spectra on top of the solid-weave and then make a spliced End-Loop.
Glueless Solid to Hollow Spectra Splice Full Strength
2. Bimini Twist. Thin and nearly 100% strong, the key to successfully using a Bimini Twist in a loop-to-loop connection is to use enough twists so that each side of the loop can carry 50% of the load. In my testing, that rarely happens below 30 initial twists--I say
initial twists because about 60% of the twists you start with are used to create the top wraps, leaving only 40% of the initial twists to hold the connection. In my experience and testing 50 initial-twists is a good number. (Note, the loop-to-loop is a different application than tying a Bimini Twist to a Slim Beauty.) The final lock knot on the tag end of a Bimini should be superglued or it will loosen after a couple hours of casting.
The biggest drawback to the Bimini Twist is that it is difficult to control loop size, and large loops can catch on the guides during casting. More twists means a bigger loop, less twists means a risk of the knot slipping.
3. Surgeon's Loop. This is a quick, reliable, east-to-tie knot. And it is relatively easy to control loop size. The main drawbacks in a spinning reel application are: a) there is stress concentration where the mainline makes its first turn inside the knot, which reduces the strength of the mainline by about 30%, b) it is a knot that can hit the guides, and hang on them, and c) after an hour of casting, when the line on your spool is no longer packed tightly, it can pull wind-knot loops off the spool. The 30% strength loss is not usually a problem in 80# Spectra on a spinning reel, unless the particular line doesn't overtest (e.g. some of the PE lines).
All of the above choices will work, with some having advantages over the others. You can probably tell, I'm a big fan of the spliced End-Loop