Do you have an old bike, that is too crappy to resell, too dated to utilize or too dear to you to part with? Well, so did I!

I designed this carrier to change my old 26" mountain bike into a single speed fun and simple ride. The bike came with the classic triple crankset with 44-32/22, BCD 104/64 chainrings and 9 speed rear casette and derailleur. I have left only the middle chainring in the front and wanted to reuse the 22 teeth chainring as the single rear cog on HG freehub. This bracket fits the small chainring perfectly and is secured with four M6x30 mm hex bolts and nuts. It is locked on the freehub with regular casette lockring.

The two halves do not center the chainring on the freehub body, but rather offset it by 1 mm. That is what fit my bike well, but i do not expect it to be very different for other bikes. If your chainline is different, scale the parts accordingly - it they will get a bit distorted, but it shouldn't affect the function.

The model needs supports in the bolt head and nut holes (yea, I know I could have worked around that and made it supportless…). I printed the parts with 6 walls and 30% gyroid infill in regular PLA just for testing, but it holds up suprisingly well.

It works fine, but be wary of your chain fitment - shorten it accordingly. It will still probably be loose (unless you are very lucky with your chainstay length), so look for a tenstioner (there are even some models floating around). Without it, the chain will tend to slip off the rings on heavy pedal strokes. Last thing to note - you do not need to buy a single speed chain.