If you have a Range rover classic or early Disco 1 you will have the one piece (10 spline) shaft and (think) flange. If you want to fit heavy duty halfshafts to this axle you will need this type of flange which looks just like the "5806" but the bolt hole PCD, bolt hole diameter and the location diameter are all slightly different.
Manufactured from upgraded materials to reduce spline wear, zinc coated to resist corrosion and with spin on caps sealed with an 'O' ring.
Any spline/drive member which is allowed to run in a dry, non-lubricated condition will be subject to 'fretting corrosion' leading to failure. On early oil filled swivels oil migrated along the CV stub shaft lubricated the drive member spline, on later grease filled hubs this migration does not occur so regular attention, lubrication of the drive member spline is necessary. If you use Ashcroft heavy duty drive members it is simple to remove the cover nut, fill with EP80/90, and replace the nut, this will keep the spline lubricated.