If you end up stripping the M5 holes, you may not have any choice but to drill right through the plugs with a larger drill to tap them out to 8mm which would be much stronger. Drilling right through will be ok as the shaft has to be removed anyway and any swarf can be cleaned before reassembly. Start with a decent 5mm SHCS and remove any end chamfer to ensure the threads have the best chance of holding. If you have to resort to drilling right through, the hole can have a short countersunk screw in it as a plug.

I think the correct way to remove the cap is to screw a bolt in the hole and once the tip of the bolt gets to the shaft, the bolt will pull the cap out of the socket.

When turning a bolt in a threaded hole, a lot of the effort goes into friction under the head and between the male and female threads. This means that the bolt shank has to resist both tension and torsion at the same time. Doing it with the goal post arrangement means the M5 bolt only has to resist the tension.

When using a puller like Mikes’ it’s best to put a spacer between the parts being pulled and the bar so the centre screw or bolt can be done up tight. Effectively becomes a single solid unit vastly reducing the chance of thread stripping.

Way back young and hairy Clive stripped the thread on the centre bolt doing a similar job, fortunately not the extractor thread on the part being removed. Was advised to make things solid with a spacer and it all came out quite easily. As I recall it with less torque on the pulling bolts too. I presume with it all locked up solid the mechanical efficiency at actually pulling is much greater. Or something.

Probably unwise to use a high tensile bolt in the middle. Nice fitting ordinary bolt, something better than the rattle around big box store cheap ones, seems wise. If everything does go whaooie shape a HT bolt could well strip the thread in the part being removed. Which makes the problem ten times worse. An ordinary bolt stripping leaving the other thread intact is much less of an issue.

If need be and you have the facilities make your one with a top limit size thread for best grip. Something I’ve done in the past when I really didn’t like the potential fall out if things didn’t work.

Clive

Yet a good number of Centec 2A & 2B photos which aren’t adverts show craters around the 2 cap holes from numpties who can’t tighten a screw far enough.