A set of transgenic insertion stocks on the fourth chromosome, each containing a 'Double Header' (DH) trapping cassette in a coding intron of a protein-coding gene; generated using the technique described in FBrf0239826. The DH cassette comprises two independent trapping modules oriented in opposite directions: 1. a protein-trap (PT) module for tagging endogenous proteins, composed of a splice acceptor site, a EGFP-FlAsH-StrepII-TEV-3xFlag ("GFSTF") multi-tag cassette and a splice donor site, and 2: a gene-trap (GT) module designed to truncate the endogenous gene into which it inserts, as it contains T2A-GAL4 followed by a polyadenylation signal. Translation should skip at the T2A sequence, truncating the endogenous protein and producing a separate GAL4 protein. Depending on the orientation in which the DH cassette is inserted relative to the direction of transcription of an endogenous gene, the inserted element can either be in the 'protein-trap' or 'gene-trap' orientation for that gene. Each insertion line contains one of three versions of the cassette (Mi{DH.0}, Mi{DH.1} or Mi{DH.2}), depending on the frame required to generate a trap.