Beeswax is brilliant for waxing your linen sewing thread.
It gives your thread a water resistant coating and also makes it slide much more smoothly through the holes in your leather as you stitch. This makes it easier and more enjoyable to do your stitching, and also means that your thread won't fluff up and snag as you work.
To use, cut your length of thread and pull it across the block of wax 3 or 4 times, holding it down onto the wax with your thumb. You can do this from the middle of the thread towards each end.
This is a 1oz (28g) block of white beeswax.