The Osprey Nib-Block Kit  includes the nib-block, a small plastic dowel, and a rubber grip. The nib block is nothing but an improvised use of a regular thread spool. If you have one at home, you can use that instead. 

These convenient accessories allow safe and quick swapping of friction fit/ heat-set ebonite feeds.  They work with the Osprey Zebra G, Phosbronze flex and  #5.5 ultra-flex nib units. 

The centre hole of the nib block is too small for a size 6 ultra-flex(UF)  nib and hence does not work to disassemble #6 UF nibs.

#6 Steel, Gold and Special grind nib units  are all  fitted with a plastic feed that has an end tail, and should not be disassembled using  this nib block to avoid fracturing the end tail, instead use the soft rubber grip provided in this kit to pull out the nib and feed from these units.

For instructions on dis-assembling and assembling the flex nibs using the Nib-block kit, download the Flexpert Maintenance Guide, a copy of which is also provided when you purchase the kit.