The W90SK is a stacked version of the W90 passive ceramic magnet unit. With black covers, the stacked W90SK offers improved hum cancelling response.
About Wilkinson
Known throughout the world as a guitar 'guru' (a moniker he tolerates rather than endorses) Trev Wilkinson's comprehensive range of replacement guitar parts are what cemented his reputation throughout the industry with their simplicity, durability and problem solving designs.