I hope this is the place to ask newbie questions that are embarrassing to ask.

My background is in hand guns and I have all the normal cleaning supplies for hand guns. I went and shot my AR15 for the first time and now i am cleaning it. To learn how I'm watching a video by Jerry Miculek.  On his advice I go guy a 5.56 brush, a bore guide and a long cleaning rod.  I put the bore guide in. But my jag with the patch is too big to fit in the bore guide. The 5.56 brush will fit in it, but my jag won't even fit with no patch.  Do they make small jags?

Jags are normally sized to fit the barrel bore, though calibers very close to each other typically only have a single size like 25 cal and 6.5, or 270 cal and 7mm.
Putting on too big of a patch will also make it difficult to fit the combination into the bore.

It seems that most .22 jags are a very tight fit with a normal patch in the AR rifles.
A possible solution is to buy a .22 Rim Fire cleaning jag that are slightly smaller then .22 center fire jags.

Some people report using a .20 caliber jag works well, and some people use a .17 caliber jag, but they have to be used with a .17 caliber 5/40 thread rod because they have different threads then a standard 8/36 thread cleaning rod........

https://www.brownells.com/gun-cleaning-chemicals/cleaning-rods-amp-accessories/cleaning-rod-jags/copper-eliminator-male-thread-jags-prod44035.aspx

Personally, I lightly chuck a brass jag in a drill and run it while using a fine cut file to reduce the diameter.
It's also usually necessary to use smaller patches, and even then sometimes they need to be cut down.

Don’t know if this applies, but I as I recall I bought a .22 brush/jag/something that didn’t seem to fit whatever I intended to clean.  Turns out there are separate .22 cleaning tips for both pistol and rifle.  Things got better after I got the weapon specific tip.  Didn’t make sense to me at the time, but that’s the way I remember it.......

I have used the same jag for anything from a 9mm to a .45 ACP and never questioned it.  I had no idea they sold jags in calibers. Well, I just ordered a few caliber specific jags off the web, so I'll soon be more precise in my cleaning.  Thanks for the tip, I learned something new today.

Hoppe's has a .17-.20 jag available on Amazon, that's what I use on my .22's.

Go to Boretech. Get the .17 cal jag and every thing else you'll ever need.