I used the runer from the Devil Gundam for the pegs so compared to the kit it's not that big.

But I used 1 mm styrene rods for the finger and they are holding quite well so far.

And from my experience with it when you try inserting the rods, you should be able to feel if there is a lot of resistance between the rod and the hole.

If there's a lot you should adjust the hole by filing it or run a hand drill through the edges of the hole (this is to increase the hole size little by little).

I think depending on what sort of finish you want, using bigger rods or gunpla runer shouldn't be a problem. The only time I've broken a styrene rod was because the hole was too small (probably my tools weren't very precise).