Abstract: Th collapsible mandrel includes a core upon which the coil is wound removably secured to a pair of spaced parallel flanges. The core includes a pair of hollow, partially semicircular members each having an arc length less than 180.degree. and a pair of transition members each disposed to fill a different one of two spaced gaps between the pair of hollow members. Each of the hollow members has a plurality of spaced grooves on the outer surface thereof substantially parallel to the pair of flanges to receive the material which is to be wound to provide the coil. A shaft is disposed coaxially of the axis of the core extending between the pair of flanges internally of the core. The shaft includes an arrangement to releasably lock the core and the pair of flanges into an integral unit when the coil is being wound. Upon completion of the winding of the coil, the shaft and the pair of flanges are unlocked and removed.