Floating captive screw

Abstract

A captive screw for securing together two panels has a screw and a spring extending between the screw head and a ferrule. A collar is formed on the screw shank under the ferrule to limit penetration of the screw threads in a bottom panel so that the upper panel floats on the spring.

We claim:  
     
         1 . A captive screw comprising: 
 a ferrule having an inner annular ring on an interior surface of the ferrule;    a screw having a head, a shank adapted to pass through the ferrule, a threaded portion at the end of the shank opposite the head, and a collar formed on the shank proximate the threaded portion; and    a spring extending on the shank of the screw between the head and the ferrule;    wherein the screw is captivated on the ferrule between the head and the collar, and the inner ring is dimensioned such that the collar does not permit movement of the collar past the inner annular ring but permits the passing through of the threads of the screw through the collar.    
     
     
         2 . The captive screw according to  claim 1  wherein the ferrule has a generally cylindrical exterior surface having a plurality of knurls for securing the captive screw in a preformed aperture in a first structure.  
     
     
         3 . The captive screw according to  claim 1  wherein the inner annular ring forms a generally circular opening in the ferrule.  
     
     
         4 . The captive screw according to  claim 2  wherein the ferrule has an annular lip formed on the exterior cylindrical surface proximate the top of the ferrule for limiting the penetration of the ferrule in the preformed aperture in the first structure.  
     
     
         5 . The captive screw according to  claim 2  wherein the ferrule has an annular circumferential groove formed in the exterior cylindrical surface of the ferrule immediately adjacent and below the annular lip for receiving the plastic flow of material when the ferrule is pressed into the preformed aperture.  
     
     
         6 . A captive screw comprising: 
 a ferrule having a first and a second opposed ends and an inner annular ring on an interior surface of the ferrule, said ferrule having an annular lip at one of said first and second opposed ends and an annular circumferential exterior groove adjacent said annular a screw having a head, a shank adapted to pass through the ferrule, a threaded portion at one end of the shank opposite the head, and a collar formed on the shank proximate the threaded portion; and    a spring extending on the shank of the screw between the head and the ferrule;    wherein the screw is captivated on the ferrule between the head and the collar, and the inner annular ring is dimensioned such that the collar does not permit movement of the collar past the inner annular ring but permits the passing through of the threads of the screw through the collar.    
     
     
         7 . The captive screw according to  claim 6  wherein the annular lip and the circumferential exterior groove are dimensioned and configured for pressing the ferrule into a panel and securing the captive screw in a preformed aperture in a first structure.  
     
     
         8 . The captive screw according to  claim 6  wherein the end of the ferrule at which the annular lip is located faces the screw head.  
     
     
         9 . The captive screw according to  claim 6  wherein the end of the ferrule at which the annular lip is located faces the threaded portion of the screw.  
     
     
         10 . The captive screw according to  claim 6  wherein the inner annular ring forms a generally circular opening.  
     
     
         11 . The captive screw according to  claim 6  wherein the inner ring is formed by plastic flow of the ferrule during assembly of the captive screw.  
     
     
         12 . A captive screw comprising: 
 a ferrule having a first and a second opposed ends, said ferrule having: 
 a first annular lip at one of said first and second opposed ends;  
 an annular circumferential exterior groove adjacent said first annular lip; and  
 a second annular lip adjacent to the annular circumferential exterior groove and located across the annular circumferential exterior groove with respect to the first annular lip;  
   a screw having a head, a shank adapted to pass through the ferrule, a threaded portion at one end of the shank opposite the head, and a collar formed on the shank proximate the threaded portion; and    a spring extending on the shank of the screw between the head and the ferrule;    wherein the screw is captivated on the ferrule between the head and the collar, and the ferrule is dimensioned such that the collar does not permit movement of the collar past the ferrule but permits the passing through of the threads of the screw through the collar.    
     
     
         13 . The captive screw according to  claim 12  wherein the ferrule has a generally circular interior surface.  
     
     
         14 . The captive screw according to  claim 12  wherein the annular lip and the circumferential exterior groove are dimensioned and configured for pressing the ferrule into a panel and securing the captive screw in a preformed aperture in a first structure.  
     
     
         15 . The captive screw according to  claim 12  wherein the first annular lip extends outwardly away from the ferrule farther than the second annular lip.  
     
     
         16 . The captive screw of  claim 12  in combination with a heat sink.  
     
     
         17 . A captive screw comprising: 
 a screw having a head, a shank adapted to pass through the ferrule, a threaded portion at one end of the shank opposite the head, and a collar having a plurality of outwardly extending legs formed on the shank proximate the threaded portion; and    a spring extending on the shank of the screw between the head and the legs of the collar;    wherein said collar is dimensioned and configured so as not to permit the passing of the spring past the collar thereby captivating the screw.    
     
     
         18 . The captive screw of  claim 17  wherein the outwardly extending legs are substantially flexible thereby permitting the legs to fit through an aperture in a structure which has a cross section larger than a cross section of the collar defined by the ends of the legs when the legs of the collar are in an unflexed state.  
     
     
         19 . The captive screw of  claim 17  wherein the collar is in the shape of a crown.  
     
     
         20 . The captive screw of  claim 16  in combination with a heat sink.