(read how to identify your stamp below)
You have the 8¢ Ulysses Grant from the years 1923-30.
The first variety (#560) was issued in 1923 and has a perforation guage of 11 all the way around. This stamp can be found by clicking here. The second variety (#640) was issued in 1927 and has a perforation guage 11 at the sides and perf guage 10½ on the top and bottom. This stamp can be found by clicking here.
If you do not possess a stamp guage and are lucky to have another stamp from this same series there is another method of indentifing the number of perforations on each side. If you lay one stamp face up in front of you, on a flat surface, place the other stamp's left side next to your stamps bottom side to see if it has an exact match up of the perforations all the way down the side of that stamp. If by pointing the tips of the perforations, of each stamp, together they will touch all the way down, the perforations on that side of the stamp are perforation guage 11. If, however, the perforations do not match identically and there is a slight mismatch, then that side is a perforation 10 1/2.
The stamp has the letters Kans.
The value of this stamp (#666) can be found by clicking here.
The stamp has the letters Nebr.
The value of this stamp (#677) can be found by clicking here.
To determine the difference in the perforations between #560 and #640 you will need a copy of the very common 1932 3¢ Washington (#720). A picture of which is shown below. Follow the instructions below