Just measured the spindle bore on my Basic - it's an M14 thread so it's no surprise that it is about 10.16 bore, like the U3. If using collets to hold bar or milling cutters it sort-of makes sense to get ER16s, which do up to 10 mm. I sometimes use ER25s as I have a holder designed for the job, and on the U3 I have a replacement ram which takes ER11, giving me up to 7 mm diameter, same as the usual drill chuck but more accurate and much more compact. I really don't like the tailstock on the Basic, so I may make a new one which will also take the ER11 ram (there is an ER16 version available too). As for the milling cutter, the motor is only about 40 W, so you won't find much use for a cutter above 6 mm, I would have thought. There are some DC motors that will fit and claim over 100 W power, but I haven't tried one yet. I intend to fit the Basic with modern high torque stepper motors and a substantial spindle motor in the hope of getting a useful NC lathe out of it.
