I remember when a fella came into work and wanted a set of glow plugs for his 300 tdi, no poblem i said - went and got them off the shelf, came back and he says " ive taken the old ones out already, is it ok if i just match them up to make sure they are the same?" no problem i say.
So he pulls a bag out from his pocket and pulls one out, has a look and says "hmm they arent the same mate, look" - to which i turn around and look, and inform him that he's removed his injectors and not his glow plugs...... the look on his face......