help with vdo gauge fitting kit /bulb

[steveo3002]

ive got a new vdo 150 035 001 G boost gauge , it needs a bulb holder and i need to know the threads for the fitting onto the boost pipe

cant seem to find any info ..the bulb holder goes into a plain round cut out , not notches for it to clip into etc

anyone know anything on them?

[steveo3002]

pic of the threaded boss ..its approx 12mm dia