The following comes right from Craig (sewerat) who made our sweetass flush axles...
INSTALLATION INSTRUCTION FOR FLUSH MOUNT AXLES
1) RAISE BIKE FRONT END UNTIL TIRE IS ¼” OFF THE GROUND.
2) REMOVE THE FRONT AXLE. Remove front wheel
3) WITH THE CONTAINER OF ANTI-SEIZE PROVIDED, APPLY ANTI-SEIZE TO THE NUT CAP, AND NEW AXLE SHAFT.
4) INSERT THE NEW THREADED FLUSH NUT CAP UP TO THE KNURL IN
THE LOWER LEG.
5) Included in your kit is a puller for you to use, use this in place of the axle, slide the puller thru the fork lower, thread the axle cap all the way onto the bolt, gently tap the end of the cap into the fork lower with a rubber hammer, tighten up the nut to make contact with the fork lower. As the new axle nut moves in make sure you have the bolt seated as far as possible into the end cap, then continue to seat end cap. Proceed to tighten the nut until the axle cap has seated in the fork lower, remove the puller, re-install the new axle.
6) USING A TORQUE WRENCH AND A 9/16 SOCKET, TIGHTEN THE AXLE
TO 55 FOOT POUNDS.
7) PLACE THE FLUSH MOUNT HEX COVER END CAP IN THE PINCH CAP
SIDE, HOLDING IT FLUSH IN PLACE, TIGHTEN THE PINCH CAP.
NOTE: IF THE NUT CAP WILL NOT FIT INTO THE LEG (3) FOLLOW THESE
WHAT HAS HAPPENED IS THAT THE ORIGINAL AXLE WAS SO TIGHT THAT
IT MUSHROOMED THE OUTSIDE EDGE OF THE AXLE HOLE, MAKING IT TO
SMALL FOR THE NUT CAP TO ENTER. MEASURE THE O.D. OF THE NUT CAP
AND USING THE SAME SIZE REAMER, RUN THE REAMER THRU THE HOLE
TO CUT AWAY THE MUSHROOMED EDGE. DO NOT TRY TO USE A DRILL
Refer to this link as well for some pictures
I also highly recommend that with every oil change you take you front axle out, and re-apply a thin coat of anti-seize onto the axle. If you ever have the axle get stuck into the front wheel, you are going to have a hell of a time getting it out, as you can not use a drift pin from the other side to push it out like a normal axle would be able to do.