Jerry Kaidor:
Does anybody know the exact part number of the screws that fasten
the heated pitot tube to the “tower” on a C23? They seem to be
fillister head, equivalent in diameter to #6, but they are finer
thread than 32TPI. Probably NF 40TPI, although I didn’t have my
thread pitch gauge with me.
As it does in so many fine details, the Beech parts book glosses
over this one; there is no listing for these screws.
My best guess would be something like: AN501-640-??… Wait,
those are slotted, and the ones on the airplane are phillips head.
The Cessna dealer across the field was only able to come up with
flush-head countersunk ones.
The screws have 6-40 threads. Many owners and inexperienced mechanics have buggered up their Pitot tubes by forcing 6-32 screws into them. The correct screws are not only a 6-40 (#6, fine thread), they are also quite short.
Countersunk Phillips in stainless are MS24693C224; cad-steel are MS24693S224.
Pan-head Phillips in stainless are MSMS51958-27; cad-steel are MS35207-227.
They are hard to find in stainless steel. RAPID has plenty of the pan-head cad-plated MS35207-227 screws (the stock type) for eight cents per screw; there may be a minimum purchase quantity. Genuine Aircraft Hardware may have some; they were out of stock when I last checked earlier this year (to restock my bench stock). Here is the link to their PDF page on these screws, if it works. Their main link is on the BAC link list.
http://www.gen-aircraft-hardware.com/images/pdf/pitot_drive.pdf