What's the diameter of the shank of those 5mm cutters you pointed me to? Also flute length?
shank=5mm
the blade is about 10mm with about 5mm clearance above that (15mm cut depth)
theres aprox 20mm of clean shank to grip onto
13mm of coarse (1.3mm pitch) thread 5.7mm diameter

check your er16 5mm collet to see how much shaft you need