I'm going to spool my wife's casting reel for her and just wondered what pound test of mono you'd use for 50lb. Power Pro braid?

It doesn't matter. Any size you have lying around will work. Heavier line will require a smaller amount than thinner line.

What ^^^ said.  I picked up a spool of cheap mono on sale one time just for this purpose.  All it does is give you filler, that's it so nothing fancy is needed.

What everyone said, get cheap mono.

I just use 8lb trilene and a double uni for everything. 

 

If you have 10% more main line than you can cast, you'll never dig into your backing unless you hook a Jeremy Wade-tier carp or catfish. Especially with 50lb braid. 

I use 12 pound big game because it’s cheap and I bought a spool for cranking but didn’t like it. I will usually crank the handle about 60 turns then put my main line on.

Does  it matter, no

I like old braid.

It is light and the connection knit is smaller

.....additionally, if I am getting spooled, I would rather have braid tied to the reel.

I use tape vs a knot to connect to the spool incase that happens

Thanks all! Yeah, I have a ton of different Big Game spools I picked up at Wal-Mart on clearance for $1, 8lb., 10lb., 12lb., 15lb. and 20lb. I already have the 12lb. spool open so I'll probably just use that. Thanks again!!!

I would only add that other than just using a basic line, certainly not a premium one at a premium price, I'd likely want the monofilament to more or less match the diameter of the braid main line I'd be tying to. 

 

50 and 12 sounds about right, will make for a nice junction knot.

 

Brad

I would get the cheapest you can find.  Lb test doesn't matter at all.

I use 14 pound Stren Original mono on all my reels. It is not as cheap as some and not expensive as others, but what it is is a QUALITY line that I can rely on if I get bit by one of the Chesapeake Bays larger rockfish (stripers), a big blue catfish or one of our big snakeheads. Those last two can partially spool you quickly. SO I want a line I can trust on the back end of my braid or fluoro line. The Big game you have is fine also.

 

I spin my old mono and fluorocarbon line off with a drill on to an old spool. Use it for filler when needed.

16 hours ago, Burros said:

I use 12 pound big game because it’s cheap and I bought a spool for cranking but didn’t like it. I will usually crank the handle about 60 turns then put my main line on.

Exactly what I use and for the exact same reason too!

I use 12lb Zebco Omniflex mono that I buy from Walmart for like $1.75 a spool....for 700yds. It's cheaper than dirt and is thick enough I would trust it to some extent if I ever got down to it. 

Inexpensive 10lb .013 dia mono at Walmart.  I tried smaller diameters, but found to be the best base for everything for me.