The synthetic M14 Stock used a screw bolt, nut, and nut retainer in lieu of the wood screw used on the regular wood M14 rifle stock.

     Here is the complete unit - the bolt, the nut, the nut retainer - used, but in good condition.

     You will need this screw if you want to switch to the reccomended synthetic stock (waterproof and TOUGH), as the wood screw from your old stock simply won't work!