Bolt Spacers that can be cut down to the needed size.
 
While bolting the splitters on to the bumper, many times you will need to space out the splitter from the bumper as most bumpers curve upwards.  these spacers can easily be cut down to the size you need and can help secure the splitter edges to the bumper without you having to stack washers on top of washers to fill the gap.
 
Provided in pack of 2, the spacers have approx 1/2" ID space for use with self tapping screws or bolt and nut combination. each spacer is approx 6" long so you can cut it down to the size you need with simple tools.