Used the proper terminology, `lock out dial' as you gave me and got a good video showing it just as you said. Was trying with a screwdriver, but just felt something was going to break so backed off. Will give it a go again later. Thanks.
That cap was covered in much underneath but came off in the end. The video's then show that the 5 mm allen bolt must be checked for tightness.
Sadly mine will not tighten and so when continuing to put the 4 mm in nothing happens. I am guessing I need to take the whole bit out.
Am I correct. thanks.