These are the two countersink screws of the type used on pre-war up to 1947 OHV and Sidevalve Norton single engines, which screwed into the inner timing cover behind the magneto chain.
Unlike the 1948 onwards OHV/SV engines (which used shallow head bolts in this area), these screws were countersunk to avoid fouling the magneto chain.
It was normal practice to tighten them as much as you could with a screwdriver, and then use a centre punch to punch the soft aluminium of the inner timing cover just next to the slot of the screw - then a little bit of alloy would mush out into the screwdriver slot to stop it coming loose. I will leave it to you to decide if you wish to do this - or use a modern threadlock. However it is good practice to use one of the two methods to stop the screw coming loose.
Original Norton screws were used as the template to make these, and they fit nicely in the original timing cover countersinks, as can be seen from the photograph.
As these tended to get over tightened or chewed by previous owners, original versions of this screw are now hard to find and normally have their scredriver slot chewed up. We have made these screws from stainless steel - which argueably is not necessary, as they are in an oiled area - but we make a complete cheesehead set for these timing covers in stainless - so it is logical to continue that material to these screws, and remembering that our stainless steel is stronger than normal tensile strength plain steel screws, these shoudl be more durable.
Note, we also sell a pair of these screws as part of the entire 38-47 Timing Cover Cheesehead Set (Item 1000), in case you wanted to replace the full set.
These screws are shown fitted to a 1938-47 style engine - but the same part number countersunk screw was also fitted to the pre-38 style OHV/SV type engine style. I am not sure what date these screws were introduced, but would estimate it was circa early 1930's - email if you need to confirm dimensions if you have an early 30's OHV/SV engine and want to make sure