Hi John,
I need it for one of my Cobras 3520/12.  These motors have four M3 threaded holes to mount https://innov8tivedesigns.com/parts/motor-parts/cobra-c-35mm-bolt-on-prop-adapter-4-hole and these holes can be used to mount the fan. 3 bolt version of the fan for 28xx Cobras will unfortunately not fit.

I know that fans for 35xx series existed but are hard to find.

Thanks,
M

I believe I bought the last one like 4-5 years ago, As I called him directly and he had to dig that one up for me and said they were discontinued already for a while at that time. These only fit the older 3 screw versions of that motor and not the newer 4 screw versions. In any case this is what they look like. Excuse the scratches. This is for the 35 series. The 28 series is pretty much the same only smaller. Just a side note that I found it pretty ineffective on the 28 series as the motor seemed to run hot regardless in full fuse planes and on the 35 series I ran it with and without the fan and it ran cool, did not see much difference there either. Maybe it was more effective for helicopter guys? Just a guess.