Bicubic interpolation can be accomplished using either Lagrange polynomials, cubic splines, or cubic convolution algorithm. This has replaced hobbing for some involute gears and cutting external splines and slots. The 12-spline flange screw drive has twelve splines in the fastener and tool. Bicubic surface patches, defined by three bicubic splines, are an essential tool in computer graphics. Mechanically, the gears are equivalent to rotating splines with modified profiles. Some trees can accommodate higher order primitives such as splines instead of simple triangles. Some radial basis functions such as the polyharmonic splines have no shape-parameter. It is essentially a beefed-up square taper spindle with splines instead of tapers. Multivariate and Adaptive Regression Splines model almost always creates the basis functions in pairs. Some cranksets feature modular spiders, where torque is transmitted through splines. The Octalink system uses a spindle with eight splines. Hermite splines are named after Charles Hermite. The name comes from the use of orthogonal polynomials in the state and control splines. An important concept associated with regression splines is that of a knot. Derivative filters based on arbitrary cubic splines was presented by Hast.