45 the locking strip 47 as shown in fig5 and 6 is of open arrow head configuration with oppositely directed base flanges and is capable of being pressed down onto and locking together the two adjacent hooked side flanges 43 of the two parts of the tube forming strip 41 the locking strip is applied by feeding it from the locking strip guide 48 through the opening 34 of the first of the pressure rollers 37 and between its annular ribs 39a the reduced diameters of which allow for the thickness of the base flanges of the locking strip superimposed on the base portions 42 of the adjacent tube forming strips 41 for better interconnection of the convolutions of the tube forming strip it is preferred that glue be introduced into the open arrow head part of the locking strip this is done by a glue nozzle 49 extending radially into the round section passage 50 in the locking strip guide 48 through which the locking strip passes the glue pump 32 draws glue from a reservoir not shown by way of a hose 51 and delivers it under pressure to the nozzle through a hose 52 with continued rotation of the core 20 the helically wound tube forming strip 41 its adjacent convolutions locking and adhesively secured together by the.