This is an optional Exotek SRX-2 Aluminum Caster Hub Set. These heavy duty 7075 precision machined alloy C-hubs have been machined down to 12 grams per SET, but are much stronger than the stock hubs. The hubs are also polished and anodized in factory Serpent orange and laser etched for easy left / right identification.
The C-hubs with the 2mm spacers (included) matches the stock SRX C-hub geometry. With the vertical ball end mounting, roll center adjustments are easily made by adding or removing spacers.