through axle adapter - what size?
 

just picked up my 1st fattie, 2014 Mukluk 3 with bluto front fork. I am stoked to go play - but - need to convert my standard fork mount bike rack to work with my through axle. I'm not familiar enough with measurement/sizing to know what size through axle adapter to buy. [picture below] Can someone please point me in the right direction?
https://cimg5.ibsrv.net/gimg/bikefor...b2519c9e9f.png