I have som old 12 lb bass pro brand mono that has seriously bad memory issues that I want to use for backing. Would 12 lb mono be suitable for 50 lb braided line?

Yes

yes, I use either 12, or 20lb mono.  Depends on the reel which size mono.  Deep spools get 20, shallower ones get 12.  Then about 100-125yrds of braid.

If you have the chance of getting into species that can run -like stripers- mono backing is a good idea. Otherwise I just use kite string.

Will work fine, I use whatever I have on hand for backing for braid.  All you doing is taking up spool space.

I match diameter usually. I don't know why, but I just do.

1 hour ago, Robert Riley said:

I match diameter usually. I don't know why, but I just do.

I do to,  you can find really cheap mono to spool up and just make a long cast then cut your backing and spool on main line. I hate guessing and estimating how much backing to cut.

Go to WM and buy Zebco brand inexpensive spools of mono for approx. $3.00 ea. I buy #6 lb. ~ #8 lb. for Spinning reels and #12 lb. ~ #15 lb. for Bait Caster reels. Works great as braid backing !

I also use braid as backing and use 75yds of FC.

 

I use literally whatever I have on hand. I just spooled a new ***, all I had was high end flouro, so its backed with that.

9 hours ago, ChrisD46 said:

Go to WM and buy Zebco brand inexpensive spools of mono for approx. $3.00 ea. I buy #6 lb. ~ #8 lb. for Spinning reels and #12 lb. ~ #15 lb. for Bait Caster reels. Works great as braid backing !

That's what I do too. I like to have a line that if I get low enough on braid and am casting the backing line out, at least will hold up until I get a chance to spool up some fresh braid. 2 re-ties into the day on a reel that's getting low, and...poof....your down to having some backing line out on a long cast would make the day ruined if the backing line was just some ol' junk..............The cheap zebco line is not much more than junk, but it's usuable in a pinch.

I use 15# Big Game mono. But anything's fine. The larger the diameter, the less you need. But bigger that 15# gets hard for me to put a uni knot in.

12 minutes ago, the reel ess said:

I use 15# Big Game mono. But anything's fine. The larger the diameter, the less you need. But bigger that 15# gets hard for me to put a uni knot in.

I use big game mono period lol .

14 minutes ago, EricTheAngler said:

I use big game mono period lol .

I still use it for treble lures like Rat L Trap and Spook. It's a good value and very tough. My buddy still uses it for everything.

I started using braid a while back for single hook baits and it cut down greatly on lost fish (heartbreaks). And it's not as expensive as it seems. Using mono for backing, I can fill 3 BC reels with one 150 yd spool of PowerPro 65 lb. I know 65 lb seems extreme, but it's only the same diameter as 12 lb mono. And fish seem to keep biting it with no problem. And it lasts for seasons. I can reel it off one reel onto another and I'm using the new end.

10 minutes ago, the reel ess said:

I still use it for treble lures like Rat L Trap and Spook. It's a good value and very tough. My buddy still uses it for everything.

I started using braid a while back for single hook baits and it cut down greatly on lost fish (heartbreaks). And it's not as expensive as it seems. Using mono for backing, I can fill 3 BC reels with one 150 yd spool of PowerPro 65 lb. I know 65 lb seems extreme, but it's only the same diameter as 12 lb mono. And fish seem to keep biting it with no problem. And it lasts for seasons. I can reel it off one reel onto another and I'm using the new end.

Oh I use braid. On most of my spinning rods either straight braid or with leader. I just dont like it on baitcasters because im get good at baitcasting, just ever now and then a massive backlash happens and I always seem to never get braid backlashes out. 

I buy the cheapest mono I can find for backer. Right now, I'm using 8 lb. Mr. Crappie.