This is what the email said....
Starting with the CK . "CK" designation, you are getting the same part. The CK are Moogs Premium line of control arms. Utilizing their "problem solver" technology, these control arms address common factory design issues providing a better than the original replacement for your vehicle. Most CK control arms include ball joints that are powder coated metal with gusher bearings giving them a long life. Many of these ball joints are serviceable and have grease fittings. The CK arms also have problem solver bushings and a precise fit and form for easy installation.
The RK series is a more value-driven part. Because there are so many different vehicles both foreign and domestic, Moog has introduced the R-Series arms to provide replacements for a wide range of vehicles. The RK arms have OE fit and form geometry alignment, with pre-installed OE style bushings and most include the ball joints. However, these ball joints are not serviceable like the CK arms. All of the R Series arms have Moog validated construction and design, providing a less expensive
Each line of control arms has Forged Steel, Stamped Steel, or Forged Aluminium arms to provide the best style for your specific vehicle. The Premium CK line has a
limited lifetime warranty, and the RK has a 3 year warranty that are both handled through our awesome customer service team at DST. Whether you are looking for a "light on the wallet" OE replacement, or a "premium" control arm upgrade, Moog control arms are a great choice for your vehicle.
Tammy
Customer Service Specialist
So take it for what it's worth.