Gripfid
The gripfid is an invention of knotting expert Stuart Grainger. It is a small knotter's fid with an added "grip", a hollow shaft that ends near the point with a vee that acts as a jamming cleat. For ply-split braiding the point  separates plies, and another cord is tucked into the hollow shaft of the gripfid and pulled back through the split cord. Although a latchhook may be used instead of a gripfid, the latter is much preferred. References

Knots
Textile arts
Braids