element 110 and locking groove 112 as shown in fig2 may be combined with any of the structures as shown in any of the other embodiments disclosed herein in order to assist in maintaining a secure connection between the elements in one embodiment the extension 114 is affixed to the subfloor by a means for securing the securing means may be for example a mechanical fastener or a chemical fastener through for example boss 134 as used herein a mechanical fastener is any device which joins the elements with e g pressure and includes but is not limited to a nail screw staple claw clamp barb cant hook clapper crook fang grapnel grappler hook manus nail nipper paw pincer retractile spur talon tentacle unguis ungula brad nail point push pin and tack additionally a chemical fastener is a component such as a sealant or adhesive and includes tapes glues and epoxies this extension 114 may also attach to the track the embodiments shown in fig2 35 each have an extension 120 of the second member which extends below the foot of the molding in such embodiments typically the second member is a stair molding and is secured to the subfloor the t molding is.