Here is a part diagram of the bars of a '98. I forget which year you have. The bars did change slightly from year to year to adjust ergonomics, I think 98-99 was the highest version for more comfort.
Anyways, point is #7 is the inner weight you refer to. It is made of cast ally and is in a water trap (no drain hole) so unfortunately over time it can corrode, but it's not a problem on this part. It is damped against vibration by rubbers #9 and #10. The whole assembly is only held in by spring clip #11. When you remove the inner weight (who knows why you would except to replace an accident damaged part) you almost invariably will bust spring clip #11 trying to get it out. If you are particularly cheap or unknowing or too proud to ask on a forum (sounds like your bike's PO was all these things) you might try and put it back together with a broken spring clip and hope the friction of the rubbers will hold it together. Well, it won't. So you need a new inner weight now, and the rubbers, and the spring clip. It'll probably be cheaper to get a complete clip-on from eBay to be honest, plus then you have a spare for if/when you lay the bike down. Even a parking lot drop can bend a clip-on pretty easy. You will notice the weights in both sides are symettrical, so I recommend get a RHS bar if the choice is yours, as a bent RHS bar will stop you riding b/c the throttle won't move correctly, so it's the more important to have a spare of if you don't have both. Obviously, go to your honda dealer and get one or two of those spring clips also.
I wouldn't bother with race clip-ons unless you like cramp in your wrists and trying to look through the top of your new full-face helmet, which is also going to give you a sore neck. Just get the stock ones working right. If you get stock working right, you'll also avoid industrial white knuckle (exaggeration) due to the damping weights. But seriously you can get numb hands from vibration after a while especially if you find your bike's tingle frequency is highway RPM - aftermarket bars don't have any weights in, because they are for racing and weights are heavy. So are wheel balancing weights would be my argument but whatever. For the same reason, get stock bar end weights or for example some are sold on eBay as heavy or anti-vibration bar end weights. The aluminium aftermarket parts don't do ****.
As far as #16 goes, these are just m6x65 countersunk screws, I recommend going to eBay and buying a pack of stainless allen screws
, these look nicer, don't rust and the allen head is easier to use and less likely to round out. I just searched for you, turns out no-one is selling this stuff in north america, god bless you crazy guys for sticking stoically to the imperial system! Anyways. These screws should be sealed in with a few drops of blue threadlock, don't overdo it but don't forget it either or you will keep the inside weight but lose the outer.
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You can open up the pages for each year model and cross-check part numbers. I'm helpful, but that's boring and ICBA