Cylinder head oilway question?
 

I was looking at these this evening and a size 4 allen head bit is too small and a size 5 allen head bit is too big, I was not aware you could get .5 sizes in allen keys/bits?

Most likely either imperial or a BA size.
Could even be a whitworth size!!
tabetha

Try a 7/32 AF allen key its about 5.52 mm
AF is a common size in taper plugs
ie BSPT / NPT ect
hope this helps

dooge

Thanks for the help guys, I've ordered myself a set of imperial/AF allen keys. Also found out you can get allen keys/bits in .5 sizes