There are actually five (5) distinct types of bayonets that are "correct" for a U.S. Rifle, Cal. .30, M1, depending upon which was authorized for a particular point in time.
MODEL 1905 BAYONET, WWI-Era: Originally designed for M1903 and M1917 US Rifles, this was first type to see use on the Garand. They usually came with a canvas covered, wooden scabbard. The bayonet had a bright blade until about 1917, after which they were parkerized. Later, during WWII, almost all of the earlier "bright blade" 1905 bayonets were parkerized too since it cut down on reflection in combat. These are very hard to find and are very collectable. The blade was 16" in length and each bayonet had its own serial number, along with a manufacturer's name or code and date stamp. The grips were made of wood.
MODEL 1905 BAYONET, WWII-Era: These are identical to the WWI bayonets except they were parkerized from the start, are rougher in appearance and finish and were equipped with black or reddish plastic grips rather than wooden ones. They have no serial numbers and are dated either "1942" or "1943." Many call this the Model 1942 bayonet, however this isn't the official name. These bayonets came with the M3 olive-drab fiberglass scabbard.
I've not run across either WWI or WWII M1905 bayonets in some time except in private collections, and those weren't for sale at any price.
BAYONET, M1: In mid-1943 a new bayonet was ordered with shorter blade of 10" length. It was identical to the WWII 1905 except for the 10" blade. A shorter M7 olive-drab metal/fiberglass scabbard came with it. A very few were dated 1943; the vast majority are undated.
MODEL 1905E1 BAYONET: In 1944-1946 many of the WWI and WWII 1905 bayonets were reworked by cutting them down to a 10" length. Depending upon who did the modification, the ends were reground to either a spear or clip point. Any wooden grips were exchanged for black or reddish plastic types. This bayonet would fit into an M7 scabbard, or into a modified M3 (cut down to the shorter length).
BAYONET, M5: In 1954, the bayonet for the M1 Garand was completely redesigned. It came with a 7" blade and was made in several sub-types: M5, M5-1 and M5A1, which reflect just minor differences in construction. It used the same M8A1 scabbard as issued with the M4 Carbine bayonet.
Note on the M5/M5-1/M5A1:
The most desirable are the WWI Model 1905 bayonets. Two years ago I was offered a WWII Model 1905 for $90 but I passed. Today I'm given to understand the price would be much, much higher, if you could find one for sale to start with. Yes, I've kicked myself over this ever since.
I wouldn't even hazard a guess on a price for an WWI Model 1905.
There are many 7" M5 types around today. Many of these are repro/clones that were made by the ROK (Republic of Korea) for use when their armed forces carried the M1 Garand. These clone M5 series bayonets can be found most anywhere at quite low prices. I've seen them running well under $20.
Hope this info helps.
Note on Korean War M1 Bayonets:
The correct bayonet for the U.S. Rifle, Cal. .30, M1 for the KOREAN WAR PERIOD, 1950 thru 1953, could actually be either of the following; note that both are "hold overs" from World War II.
Bayonet, M1 with M7 fiberglass scabbard. It has a 10-inch blade. The fuller was 5.75-inches long and began 3-inches from the point. The blade tip ended in a spear point and plastic grips, black or brownish in color, were installed. Production of this bayonet type began in mid-1943 during World War II (as mentioned above).
Bayonet, M1905E1 with M7 fiberglass scabbard Between 1944 and 1946 the US Govt modified many of the earlier 16-inch M1905 Type 1 and Type 2 bayonets by cutting the blades to 10-inch length and regrinding the tips to either spear or clip points. They're easily ID'd since the blood groove runs out past the blade tip. There is some evidence to support the claim that once these essentially World War I vintage bayonets were modified to the 10-inch blade length they became mixed with the Bayonet, M1 in the US Govt logistical supply system of the day and were also called Bayonet, M1. Technically this was incorrect as the official designation is M1905E1. Many of the 16-inch M3 scabbards that matched the 16-inch M1905 bayonets were modified to accept the shorter 10-inch M1 and M1905E1 bayonets.
If the correct bayonet used during the Korean War (1950 to 1953) is what you're looking for, you want either the M1 or M1905E1 with 10-inch blade.
Many are going to tell you the Bayonet, M5 with its 7-inch blade is the correct Korean War bayonet to match the M1 Garand. This just simply is not true. This shorter-bladed bayonet wasn't developed until 1954, the year after the end of open combat in Korea. This newer 7-inch bayonet (with the M8A1 scabbard) did indeed make it to Korea where it saw use for something like 20 years (maybe longer) with both US and ROK armed forces, however it wasn't on the scene until after the end of open hostilities.
For those rifles that may have fought in combat in Korea between 1950-1953 then the M1 or M1905E1 are "correct." If the rifle served afterwards then the M5 is probably a safe choice. Naturally there would've been some degree of overlap until such time as the older M1/M1905E1 types were phased out and replaced by M5 bayonet type; maybe a year or two? Who really knows for sure.
Hope this is of some help to you.