The Home Machinist!

Quick change tool posts are advertised to fit a range of lathe sizes and more than one size is said to work with a 13" swing. Are there any advantages to going for the larger size or smaller size? Any advice?

Too big on a small lathe and you can't get your tooling to easily adjust down to center.
Small tooling on a big lathe isn't so bad.

Generally an A series tool post is good for up to a 11 or 12 inch lathe

If it were me I would get the B series. I have an A on an 11" Rockwell and its shimmed up a touch between the tool post and the lathe.

I had a BXA on a 12x36, and it seemed to fit.

I too would say BXA. My Chinese 12X36 has a A which is perfect. My 12X36 Clausing needs a 1/2 spacer under the tool post with a A series. Of course I don't use Aloris style anymore,Multifix is my choice.

Yes and when people research lathes they don't always investigate " swing over tool rest / compound slide" distance. The quality of the iron determines the thickness of these parts. Fair to say that slides are thicker on imported machines because they Have to be or would freakin break.
Who knows a 12" swing has barely enough clearance for the original turret unless you milled down everything.
Good semi steel is Lower. Maybe they foresaw the newer QC tool posts.

If the quick change tool post and tool holders are dimensioned on the manufacturers website or the tool dealer shows them then using what the Aloris or Dorian website shows about sizing a tool post and the tool holders works well. You still need a few measurements from your machine to figure it all out, but it's pretty easy. I'm convinced all the off shore quick change brands were cloned from an Aloris or Dorian system anyway except for the new multifix and they were a copy of the originals as well. Anything you can do to help rigidity always helps, but it can be over done with a quick change tool holder. Going a lot larger than needed even if it fits and can be adjusted low enough can sometimes bite you. Tougher to get the tool tip close enough to the shaft face when a live center is being used, takes up more room so the tool holder / tool post can foul the chuck or even tailstock casting a bit easier sometimes, obviously the larger costs more for each tool holder added and maybe a few more I've missed. A few old timers on the Practical Machinist site have mentioned they still keep one of the old school rocker tool posts and a set of tool holders around for a very few jobs where using it can get the tool in where a quick change system wont work. From that my opinion got changed that a quick change can't do everything possible, but so far I've not run into that problem yet. I could see it happening if the workpiece or what your trying to do was different enough. My 11" lathe has a tee slotted cross slide so is thicker than usual like Spro says. The exact same tool post and holders on my 10" lathe fit it better and left me with more adjustment room than the slightly larger lathe has, that extra thickness for those tee slots makes a big difference. Most replacable tip 1/2" tool shanks are right on the ragged edge of what I can use and still get the tool holders low enough without milling some off the bottom of the holder. Figuring out some general dimensions first might be a good idea before deciding on what you and your machine needs. There's more and better selection once you get above that 1/2" tool size for not much more money so the maximum size the tool holder will take and still be low enough comes into it as well. For home sharpened HSS it doesn't really matter since you can always grind to get the tip low enough and the smaller tool bits are cheaper and a lot faster to shape from a tool blank. AXA is usualy mentioned for 9"-12" lathe size so unless you've got something out of the ordinary on yours then I think Johns right about that BXA. Going smaller than needed can still work, but the tool holders are then right at the top of the dovetail or part way out of it and rigidity is a whole lot less unless you add a block under the tool post and it stll wouldn't be as rigid as the larger and correct sized one.

I don't own an ENCO 13x40, but in their catalog (yes, I still have one) it looks to be pretty much made from the same machine as the Grizzly G0776 is, with a few different accessories. The Grizzly comes with a BXA QC tool-post and uses the 200-series holders.

I started to look at ordering but see there are a huge number of brands available. I'm just at the level of getting away from using shims so am not looking at the top of the line models. Are there any recommendations as to which China brands may be better or are they all pretty much the same.

https://allindustrial.com/all-industria ... 00-series/
This is a wedge style post,I have bought there products before and consider them to be good quality import. In fact I need to order a BXA set for a friend of mine in the next several days. And under $140 shipped as of today.

BXA works well for 13" swing lathes - have them on both lathes. The wedge type is preferred over the piston, seems to hold tightness better. I have had a Phase II brand unit for many years - it is fine.

I currently use an AXA on my 13x40 Grizzly G0776.

I used to use a BXA. I build airguns, and I found my view almost always being blocked by my BXA toolpost when working on all the small parts. The AXA fits perfectly, and let's me get a really good view of the work.

One other plus to the AXA for me is also that the smaller tooling takes me substantially less time to grind, and the blanks are cheaper.

An extended tool holder is ideal for tight spaces and small parts. They will take any sized tool you wish.