ululi1970 -- I use the HK metal trunnion retracts #225000018. The nose gear on my Dirty Birdy is 225000017. I also put a strut on the nose gear and made it work, 344000013. I think if you search these numbers on HK web site, the correct items will pop up. Any problem, let me know, I'll send the link directly.
When I first set up the Birdy I couldn't figure out how to put an electric on the nose because it was tight in there and I couldn't find a product that worked. If you read the article I did on it in modelairplanenews.com you can see how I solved it originally, which wasn't really satisfactory. I kept at it and HK finally came out with a nose gear that fit. I don't use the steering tab they include with the retract. I put a pull-pull on mine, and use 40 pound test fishing line on it. So far, works perfectly.
I use Top Flite struts made for the P-47 or the Mustang 60 on most of the retracts in my planes. 5mm, they plug right in. They cost about $10 for a set. They are tough too.
There's no doubt that the larger planes need strong gear. Robart and others are definitely rugged but very over-priced in my opinion. When I was learning to land my AT-6 I tore up at least two sets of the stock gear that was included in the kit. After 10-12 flights, we put "U" shaped plywood plates over the plastic frames. That did the trick. But electrics are so much better, and I swapped out the mechanicals for the HKs and never went back. Be careful using heavy Robart struts with the HK electrics. If the HKs have a weak link, I think it's the worm drive. The metal seems like it would strip easily if the gear gets jammed and gets banged hard. On my H9 Spitfire I put Robart struts on it originally but they seemed too heavy. I took them off, put the HK struts on because they are lighter. I generally use foam wheels. Robart scale wheels are nice looking, but weigh 2 or 3 X the foam. I've also taken to putting the HK aluminum hub wheels/tires on some planes, and they are light, strong, and cool looking.
Two things I do sometimes with my planes. I do a loop, retract the gear at the top of the loop while inverted, and when I roll out or complete the loop, the wheels are retracted. Always draws some laughs and is easy on the gear. And second, land gently. That's the best suggestion of all.