I have seen Instructables for making sliding knots for necklaces but I wanted a sliding knot which worked in reverse. The normal sliding knot is a fisherman's knot which is the ideal knot for joining two ends of rope together.
For a bracelet the cord will be in a loop and if you tie the normal fisherman's knot and pull the ends apart the 2 individual knots will pull apart and the loop will get smaller and if you pull the ends within the loop the loop will get bigger. This is also really dangerous if used for a necklace as there is nothing to stop the loop from getting smaller and smaller with obvious results.
This is no use for a bracelet as the loop can get too small as I mentioned above and there is now way for the loop to lock so that it doesn't open up accidentally.
This Instructable will show you how to tie the reverse sliding knot, how you finish the ends of the cord is up to this is just to show how the knot is tied.
Step 1: An overview of the knot.
Your minimum cord length will need to be the circumference of the object it's going around, plus allow for a ~25mm for the cord in the overhand knots and then add another 200mm for the tails.
As with everything you will need to experiment with cord length as the thicker the cord the more cord will be lost in the overhand knots.
The tail length will determine how much the knots slide apart to make the loop bigger.