John letters swingmaster 2015 iron this john letters swingmaster 2015 iron has been crafted from strong and durable 431 stainless steel giving you magnificent durability and performance a deep cavity undercut cavity design gives magnificent forgiveness and distance even on off centre hitsthe wide sole design helps to lower the centre of gravity making it much easier to get the ball airborne from a wide variety of liesan attractive john letters insert in the cavity of the club head helps to