Graham Price
If the 06 has the traditional Hornby 0-4-0 chassis (which I think it does), the axle diameter should be 9/64″. EMGS stores have an 9/64″ EM axle turned to 2mm at the ends, and also a bush 2mm ID and 1/8″ OD. combining the two gives an axle for the 06 to which you can fit appropriate Alan Gibson wheels for a 1/8″ axle. The bushes I’ve used are a running fit, not an interference fit, on the 2mm axle end, so need to be soldered or loctited. The bushes are 3mm long, so may need to be reduced slightly (along with the axle) to fit the total width AG wheels set to 16.5mm back-to-back.. This can be done acceptably by turning the axle held in a hand-drill gripped in a vice, and using a flat file held against the axle end (lathe-owners look away).