Front sights must be a post or bead, but may be an interchangeable type in a anti glare tube no longer that 1.125" or larger than 0.75" OD.
Ok, easy enough...
Both legal


1,2 and 3 legal in appropriately sized tube, 4 and 5 not legal.

And the "tube"



Rear Sights - Open, receiver, and tang sights are legal rear sights, but international and Olympic sights and extended mounts are not. What are the differences? Open is a sight type, but receiver and tang are sight locations, not types to my mind. And what is an international or Olympic sight?
Open - again easy enough... all legal.


Receiver

Tang

International

Olympic

Can anyone help with the last four?

Go to E-bay and do a search for "Redfield Sight", as you go thru the listings, you will see listings for both the "Olympic" and "International" types of these sights, as compared to the standard Redfield type receiver sights,

Here, read this, a very comprehensive description of the types of various sights and how they are used. http://en.wikipedia.org/wiki/Iron_sight

The redfield suggestion helped, thanks steelshooter.
International and Olympic sights all seem to have large diameter rear peeps with tiny apertures, extended bases, do not fold, and have large adjustment knobs for two plane adjustment.


Tang and receiver sights may or may not have similar peeps, may or may not fold, may or may not have adjustment knobs.... but don't have extended bases.


If both of the above are legal the only real difference between legal and not would be an extended sight base. How does this compare to what you've seen at matches?

Derherr65, think you've hit the nail on the head regards the extended length on the Olympic and International sights.

That appears to be the issue, don't really understand the perceived problem, as the standard and Olympic/International Redfield sights are not much different, aside from the slight increase in sight radius between the two. But that is how I interpret the rules.

Certain others will pipe up if we have missed the boat.

Once the Redfield sights were listed as legal, purchased several of them for my Marlins, as believe they are of quite good quality.

Bought mounts that allowed me to affix the more common Redfield, then actually found the correct ones for a Marlin 39 and 1894, so can now go either way if desired.

Here's my 2 cents worth about sights:

This is what the NRA rule book says:

Rear sights may be open, receiver, or tang sights, mounted as originally intended. No international or Olympic type sights, or extended mounts are permitted. The front sight must be a post or bead or if changeable inserts, may use a post or bead insert only. A front sight anti-glare tube, which may be no longer than 1 1/8” to include any attachments and no larger than a 3/4” outside diameter, may be used.
Fiber optic material may be used in or on the post or bead and may not be longer than its support blade and not to exceed 1 1/8” in length. In an anti-glare tube, the fiber optic material may not be any longer than the tube or extend outside the tube. The fiber optic sights do not need to be commercially manufactured.

With that said and having shot in every national match since it began and having been on several juries at nationals, I can tell you that this sport was created with KISS in mind. Everyone should be able to shoot and it should not be an equipment race, hence the simple rules without listing 9 thousand things you cannot use they just tell you what you can use.

Best bet: buy a sight that is manufactured to fit on your rifle and shoot the match and have fun. Redfield's, Williams, Lyman or marble tang sights all work just fine. Front sight: buy fiber optic if you like them from Brownells, a Lyman 17 if you like the hood or a Marbles small bead.

I have shot with individuals who have won at nationals and they use pretty basic sights, they can just plain shoot better than most of us! Have fun!