not a screw on freewheel , not a single straight spline but a 2 stage spline in differnt sizes - how bizarre ! if i could just hook up with the rad vendor for this part , im perplexed !
It is a freewheel. You took the cogs off of the freewheel body. If you look inside the part still attached to the hub, you will see splines. You use a Shimano freewheel tool to remove it.
update : my project all started when i stripped 7th gear - fat guy pumping to hard goin up hills & not shifting down - doh ! so i contacted rad & they sent another freewheel & tool to replace it , the shipment got lost somewhere in shipping , & i was quite frustrated dealing with tech support trying to find the item , to make a story short between tyler & sam i now have a new freewheel as they basically shipped another one on my word that the part never arrived ! no where else have i ever recieved such amazeing service as i have with rad power bikes , this alone is one of the better selling points at rad not to mention the wonderfully affordable bikes ! here are some pic of the unit - enjoy ! note the slotted ring on the back that unscrews to expose pawl / clicker assembly !