This screw holds the venturi in place on most late-model "Made in Spain" 40 DCOE carburetors. This M7 x 1.0 "grub screw" version has no head, and requires a locknut (Part No WC-34710.003, sold separately). Two required per carburetor. Sold individually.
Note that the 45 DCOE, 48 / 50 DCO/SP, and most earlier "Made in Italy" 40 / 42 DCOE use a hex-head Venturi Locking Screw (Part No. WC-64840.003). And just to keep things interesting, Weber made some DCOE variants that use an internal spring instead of an external screw.