a system for attaching fins to a tubular body of a model rocket employs a base with a horizontal upper surface and upstanding fin guide plates mounted on the base . in the preferred form , the base has a central aperture that receives an engine casing projecting from the body of the rocket . each guide plate is replaceably mounted on the base , preferably by a flange formed on one edge of each plate and a guideway formed on the base . the guide plates are radially slidable in the guideways and spaced from the rocket body . the radial position of the guide plate is adjustable to accommodate a wide variety of body and fin sizes . each guide plate flange is offset laterally from the centerline of the associated guide plate to accept fins having either of two standard thicknesses depending on which face of the plate supports the fin .