"Always as well to carry a few spares of the smaller drill bits. Without them you can be sure that the one you need for a particular job is either too blunt because someone else has used it or it breaks when you need it. Spares? Keep them in a safe place so no-one else can get to them. This may be for the 5.5mm drill bit but I ordered 4.5mm as well at the same time. (I carry spares from 1mm to 5.5mm)"