The best hair bun maker, available in 2 sizes. They can even connect to each other for longer/thicker hair.  Have a lifetime guarantee.
For Average hair a Small Holdi-Locks® can make a bun. 
Longer and or thicker hair below the shoulder blades the Large Holdi-Locks® will fit better.
To make a tighter fit, wrap a Scrunchie on the Holdi-Locks® before rolling hair on it, and  or  around the bun after.
Small is 4.25" x  1.36" x .08" or  10.8cm x 3.7cm x .2
 
Double Small is 7.125" long (can stretch depending on the way it is joined)
 
For space buns use 2 Small  Holdi-Locks®. The  Clear Holdi-Ties  can be cut shorter, they work the best. (Comes with Holdi-Locks®)
 
The Holdi-Buttons go on with a slip knot. Tighten by adding a second slip knot.
 
The Hooks latch both sides without elastic if it fits without needing the extra stretch.
 
The Holdi Ties can help to determine how long your band should be. They are designed to be folded once to join both ends together. Check out the You Tube channel Holdi-Locks Hair Buns look for the playlist Fast Easy Hair Bun Tool  for detailed instructions.
 
Tangle, headache, and droop free hold. Works like a flexible perm roller. Latches easily, and comes out easily.