Apparatus and methods for use in the manufacture of a spring unit for incorporation into an upholstered article, for example, a mattress, cushion or the like. Coil formation apparatus includes a drive shaft used to control movement of a coil pitch guide member and a link member comprising a connecting rod connected to a radius arm of the drive shaft by means of an adjustable connection. A coil interlinking process comprises compressing a first coil to define a clearance extending a second coil passed the first coil via the clearance, allowing the first coil to extend across the clearance, and contracting the second coil such that the second coil engages the first coil thereby interlinking the first and second coils. Spring unit manufacturing apparatus comprises a plurality of jaw pairs each comprising a first fixed jaw and a pivotal second jaw, the pivotal second jaw being pivoted by a cam and linkage assembly that is operated by a rotary drive shaft.