HKS Adjustable Cam Gears allow fine tuning of the camshaft timing to maximize engine performance and tailor power characteristics for various driving conditions. Either with OEM or HKS Camshafts, adjustments can be made to tune an engine’s power band to the optimum RPM range for a particular application. HKS Cam Gears are made completely of anodized Duralumin with nickel plated gear teeth except for applications with timing chains which utilize an aluminum slide with steel teeth. HKS engineers chose Duralumin as the core material for HKS Cam Gears because its lightweight properties decrease drag on the engine. As cam duration and other engine specifications changes, the ideal valve timing point will also change.
As both intake and exhaust cam duration increase, the overlap amounts can be adjusted for optimum performance. All HKS Camshafts come with recommended valve timing which can be achieved by using these sprockets in conjunction with HKS camshafts. These sprockets are compatible with standard camshafts.  Precise valve timing can be adjusted and set within the range of ± 20° along a Vernier scale of 2° intervals. Each interval index is laser-etched into the Duralumin and "A" (advance) and "R" (retard) directional markers are also laser-etched on to the cam gear face.
 
Allow fine tuning of the camshaft timing for maximum engine performance and tailor power characteristics
Made completely of anodized Duralumin with nickel plated gear teeth (except for applications with timing chains which utilize an aluminum slide with steel teeth)
"A" (advance) and "R" (retard) directional markers laser-etched on to the cam gear face
Each interval index is laser-etched into the Duralumin more details on - http://www.carid.com/hks/adjustable-cam-gears-mpn-22004-an002.html?gclid=CjwKEAjw9OG4BRDJzY3jrMng4iQSJABddor1dkXxU1Rrs4NlMY5Xxp4iZtPS4qzVBaiUgddyOXDbVxoCsrnw_wcB
Allow fine tuning of the camshaft timing for maximum engine performance and tailor power characteristics
Made completely of anodized Duralumin with nickel plated gear teeth (except for applications with timing chains which utilize an aluminum slide with steel teeth)
"A" (advance) and "R" (retard) directional markers laser-etched on to the cam gear face
Each interval index is laser-etched into the Duraluminum
Fits:
RB20DE(T)
RB25DE(T)
RB26DE(TT)