after mkI version failed on Saturday, part of Sunday pm was spent making mk II version.

Drill three holes in the steerer and tap to M3. Drill and tap a section of aluminium alloy to M6 and shape to fit inside the steerer, then trim to lose wieght (final wieght 5 g). Use 3 3 x 3 mm grub screw to keep in place ensuring they do not protrude beyond the steerer. Job done.

I like it!

What's the difference between mk1 and mk2?

mk1 used a disc with a tapered edge and a thin strip of aluminium so that it would wedge itself inside the steerer .... except after a couple of rides it didn't. This one should stay put.

To use a half of an usual star is lighter and works without issues

Surely once the headset is preloaded and the stem done up the SFN (or whatever) takes no load, so shouldn't fail - In fact a friend advocates using a home made bolt through like a head doctor and then takes it off after the stem is done up....I prefer the idea of having mid ride maintenance possible!

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Impoverished weight weenie wanna-be!
Budget 26" HT build viewtopic.php?f=10&t=110956

good point - the stem holds the assembly together, still have no expllanation as to had loosened (most likely not done up correctly in first place)

usually I use a steel bolt to preload the h/s, then fit alloy bolt, in that instance I did not do that.