If you want a 1.9" or 48mm Omni-wheel I recommend these:
http://www.rotacaster.com.au/shop/48...les---r2/index
There are several Durometers available each with their own strength ratings. The 1/2inch keyed shaft variety are easy to broach to 1/2inch hex and the wheels are durable. The 12mm bore variety are also easy to broach after being enlarged to 12.7mm.
They are designed for industrial conveyors and as a result are durable. We used them on an intake we built in the Offseason and they worked well.
The strongest variety is capable of holding up to 40kg so could be so usable for drop down wheels in Drivetrains etc( I believe that these are the wheels 118 used in 2014).
If you want something even smaller you could try these which are 35mm:
http://www.rotacaster.com.au/shop-pr...ore-no-bushing I don't have experience with the 35mm type but they look like it would be possible to broach them out to 3/8 hex.
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