I bought some Siemens breakers but they don't seem to fit my panel. The bar seems to be a different length for the bus. The long one on the right fits correctly but not the left. Are there different types? How can I distinguish from the model type?
Breakers https://imgur.com/gallery/0AQWLnu

 

Looks like a couple quad breakers. The one on the left is a CTL quad and the one on the right is a non-CTL quad. In the U.S. non-CTL breakers are just sold for replacement purposes in pre-1968 panels.

CTL means Circuit Total Limiting. Quad breakers typically can be used in most panels that will accept tandem breakers such as a 30 space 40 circuit or 20 space 40 circuit panel. If you have a newer panel that has the same number of possible circuits as spaces, such as a 30 space 30 circuit panel, you cannot use tandem or quad breakers. Using a non-CTL tandem or quad breaker in a panel not designed for them defeats the design and listing of the panel and is therefore a code violation.

 

It's a new panel 40/80 spaces. problem is not whether the quad or tandem goes on, it's that the breaker on the left I cannot push down far enough to engage with the panel bar. The one on the right goes on straight away.
the slot on the left looks a little shorter preventing the terminals attaching.
the breakers on the right are also from a panel installed within the last 10 years.

 

Can you post picture of your bus bar?
40/80 should allow tandem breakers in all spaces, but if only one on the right fits, sounds like rejection tab issue.
You are not supposed to use one on the right on newer CTL panels.
As CasualJoe explained, shorter slot on the left is a rejection tab preventing installation of tandem breaker on where it is not allowed.

Your bus bar should have a notch cut out if that space allows tandem breaker.

I had possibly defective Eaton panel that was rated 12/24, yet there were no notch cutout on the bus bar preventing any tandem breaker installations.

If your bus bar has notch cut out, then you may have to apply a little more force. Some new breakers are very tight and requires significant force to install.

 

It's a SIESEQ40200, can post pic tomorrow.
the breakers came from another 40/80 panel.

Can there be a 40/80 that accepts non CTL breakers only?

 

A 40/80 panel should accept CTL breakers, not non-CTL.

 

If your Siemens load center doesn't have notch cut out and still marked 40/80, it is possible that Siemens wants you to use non CTL breakers.

As for my Eaton plug on neutral load center, Eaton wanted non CTL breakers to be used on these panels.

 

Do non CTL AFCI's exist because we're required to use those now. I thought all AFCIs were CTL.

 

Non CTL or CTL AFCI doesn't exist because CTL is only concerns tandem breakers and AFCI doesn't exist in tandem breakers. They are only available as a full size breaker.
If you don't have enough space left, you will have to replace with lager panel or install sub panel or install dead face AFCI near by..

 

If your panel is a 80/40 space, both will fit on the busbar if it is notched. I am assuming you panel will hold 60 fullsize 1 poles or 40 full size and 20 tandem breakers.