I'm new at this and it's time to put a small tool box together. I have a good assortment, but am shy of allen wrenches. My next few planes will most likely be from Horizon. That said, do they use standard or metric allen wrenches? THX

Not sure if they will definitely be metric but it is likely. The non US world is metric.

One thing to do is treat yourself to a set of ball end allen key with screw driver handles. They are the DBs.

2mm 2.5mm 3mm 4 mm and 5mm will do.

Hi!
The Ungarian brand: Hudy makes very fine tools. Have been using them for over 20 years now.
https://www.hudy.net/

get both Allen's are cheap plus there's no guarantee that the airframe and engine wl be the same

Go to Harbor Freight and order both SAE and metric. Get two of each. Put one set on the workbench and the other in your field box. You'll be glad you did!

I don't trust HF tools when it comes to these very small sizes! As far as workbench, I have a pretty massive collection of tools as I've been working on hot rods for decades. I just won't rape that collection for my field box.

Home Depot then and get a set of brand name allen apex tips. I know I prefer them to straight allen wrenches since they don't twist like an allen will and will give you more torque since the handle is larger

You definitely want the ball end hex wrenches. There are so many times when you can't get a straight shot at the head of the bolt.

I got a Harbor Freight t-handle set a few months back and so far it has been better than every name brand I have tried