There have been several threads regarding the Maynard cocking lever, which was one of the improvements contained in his patent  of 1873. Recently, I had to remove this part to replace a damaged screw and thought that some would like to see a picture of the actual lever.
The lever is marked with the rifles serial number and a patent date of Feb. 18 1872. It is 1.240" long,.255" wide and .220" at the thickest part. The through hole is .124" in diameter and apparently is designed for a 4-40 screw, as a 5-40 screw won't fit. The spring is .125" in diameter and .160" long. 
The second picture shows another hammer cocking lever removed from a Maynard rifle converted from percussion to cartridge with the 1873 patent features but by an independent contractor and discussed on this forum under the title of Maynard Action Variant.
Otto

Otto, that screw in an original Maynard should be a 5-40 thread. The nominal size for a #5 screw is .125"(5x13 +60) divided by 1000. Screws have been made slightly smaller than the nominal dimension forever it seems.

I generally make the screw size so that the lever will just pivot on it with very little clearance. Sometimes it must be made smaller so it will go thru the action. I always make them out of a medium carbon or alloy steel and heat treat them. The fit of this lever to the barrel link and hammer is probably one of the most critical fitting jobs on a Maynard to get the hammer to half cock on opening and the screw size is very important.