The straps come in packs of 3. 

These wheelie bin lid straps are great for keeping the lid closed during high winds. 
They are fastened using marine grade stainless steel 316 A4 snap fasteners, so they will not rust, even in salt water environments. 

I contacted the local council about this design and their response was encouraging. 
There would be no risk of injury and wouldnt get tangled in the loaders compared to the bungee cord and hook style. 

These snap fasteners are DOT brand, used on heavy duty boat covers and have great strength. Their snap action is tough, takes a little force to pop on and off so perfect for this application. 

Their strength
I have had these on my bins for years now and they do a brilliant job. 
When it is collection day , I simply leave it unfastened as some councils may not like having to fasten and unfasten each time. In saying that, some councils may prefer to have a lock in place that is simple and effective to unfasten to save rubbish messing up the streets. 

Fitting guide

The straps are approx 17cm long and the caps are roughly 12cm to 13cm apart.