Taylor Made RAC OS irons. RAC stands for Relative Amplitude Coefficient, a technology TaylorMade developed to improve shot-making and characterised by 'Feel Pockets' in the back of the club head. The 'OS' Stands for 'Oversize' and these are really easy clubs to hit - in fact, Taylor Made claim them to be their longest iron ever. The Tuned Performance Cartridge Delivers a high moment of inertia which helps preventing twisting of the head on off-centre hits and stability across the entire clubface. Made of investment-cast soft stainless steel, every aspect of the trajectory and spin-rate is directed toward generating maximum yardage. Aimed at higher handicappers, the RAC OS are one of the easiest-hitting irons on the market.