Prepared Fly Tyers Wax, still produced to the same wax recipe Veniard have been producing for decades. Just wipe the tyers wax against your thread for it to work, or if you want to soften a little a great tip is to break a very small piece then immerse in warm water which will soften it, stick it to your index finger and draw your thread through it as required. A simply brilliant fly tying wax and a consistently huge seller used by almost everyone who ties their own flies.
Also note wax is brittle, if small pieces break off, it can still be used, just melt it back on to main wedge for easy use.
Note : Picture shows three Veniard Prepared Fly Tyers Wax wedges, pack contains one wedge.