a danfoss orbital steering unit. basically its the power steering valve for most tractors/diggers/forklifts from 1970 -2000
its the most complicated thing with the least no. of parts i've put together for a long time.. it has a 6 tooth gear that fits into a 7 tooth housing, with a shaft that is also toothed, & the service book has 2 pics & no words on how to do it.... 5 attempts it took to get the sodding thing turning the right way.