Hydraulic hose for your application is 1/4". If using steel tubing, 3/8" x 0.036" wall.
Sorry to tell you this, but you need to redo the bracing from the posts to the front of the tractor. What you have is not going to survive a reasonable service life and risks damaging the hood when it does fail. Flat stock has a limited lateral (side to side) strength and is subject to lateral motion from vibration. Add a vibration component to a compression load that can exceed 1800 lb (820 kilos) and failure is pretty much guaranteed. The bolts holding the splice together won't like that kind of load either.
Flat stock and structural angle are not good choices for bracing when dealing with compression loads. As mentioned, flat stock vibrates, and angle has a tendency to twist. The more stable square or rectangular tubing is much preferred.
Going back to my previous pics, the red self leveling link above the arm was originally 3/4" pipe and it bent several times under the compression load of lifting the front of the tractor while back dragging material. It finally failed catastrophically at the front connection when picking up a normal sized payload and was replaced with 32 mm square tube. It has not been a problem in the past approximately 1500 hours. You can see in the pic that it is still dead straight.
All connections and structural members work in harmony make a loader strong, but the smart fabricator makes each strong enough to survive on its own, or with only a little help from the other components. Use at least 38 mm square tube from the posts and 50 mm square tube across the front of the tractor. If you go back to my pics, you will see that my bracing is overkill by a substantial margin with 50x100 mm tubing, but I have used mine for loads exceeding 500 kilos many times over a 22 year period without a single structural failure in the parts that I fabricated.
Here is a pic of the post to brace connection on my GT using a 1/2" dowel and a pair of 3/8" (10 mm) bolts. The mounting pad is welded and gusseted to the post to handle the compression load and there is no real load on the dowel and bolts except to keep the brace from sliding off the mounting pad and keep them together under the limited negative load when the bucket is forced down hard enough to lift the front of the tractor.
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Sometimes you get on a roll, sometimes the roll gets on you.
MF GC2310, Husqvarna YTH20B42T
Down for Repairs
MF1655 w/ FEL, MF1655, MF12H, MF8H, MF7H
Spending too much time on MTF to work on my toys.