Since 2004 K&N produce also oneway oilfilters in a very good quality. To satisfy the demands of racers, K&Nl filters have many features over and above the requirements of most vehicles. They use thicker canister walls for extra strength and durability which reduces the risk of damage from loose rocks and debris. The durable construction will withstand higher oil pressures found only in racing environments without bursting. The drilled hole on the nut is for a safety wire attachment. Required for many types of racing, the safety wire prevents blown oil filters from falling on the track and representing a hazard to other race vehicles. This extra engineering offers peace of mind for consumers who want only the best.