Bottom bracket advice please!

[GooseJuice]

I've been stripping down my Supergoose for refurb and dissembled the bottom bracket and crank at the weekend.  Unsurprisingly the bearings were shot to bits (pic attached) and need replacing, but I've been struggling trying to make sense of what replacements I need to order.  It's a Mongoose stamped bottom bracket and crank.  The crank needs rechroming at some point so may replace it short term so I can still ride it.  The bottom bracket is stamped with a 28 (I'm guessing it's for the TPI). What I'm struggling to find answers to is:

1. Does the TPI (which I understand is a thread count) relate to the bottom bracket or the crank to which it's threaded?

2. I'd like to retain the stamped bracket and just replace the bearings, etc inside but when researching I can't seem to find much by way of standards or sizing references to ensure the diameter of the bearing rings I order will match the existing size.

I think the below is what I need but I'd just love to better understand it.  For example, if the TPI relates to the threads in the crank then I need to be careful to ensure any replacement crank is compatible.  I'm sure I'm considering things here that I probably don't need to / don't exist!!!

https://www.boydsbikes.com/product-page/sunlite-28-tpi-bottom-bracket

Thanks all!

[oldschoolace]

pop a ball out and give it a good clean. get it under a light and see if the surface is pitted or marked. if it is treat yourself to a new set if not get em cleaned, regreased and fitted 

They are pretty standard sizes so unless you want a specific ball cage, any will do

[deeman]

you have a 28 tpi crank which needs a 28tpi bottom bracket. You only need to replace the bearings which are not threaded if you are retaining the mongoose stamped BB.....Your local bike shop will probably be able to help.....you just need standard US bottom bracket bearings for an old school bmx.  Pretty much any half decent bike shop should sell 'em for a couple of quid...
Failing that just buy a cheap bb like this and nick the bearings...i

https://www.ebay.co.uk/itm/9-Piece-Bottom-Bracket-for-1-piece-crank-Old-school-BMX-Bike-American-size/370875980092?epid=1888287623&hash=item5659ee593c:g:x2EAAOxyqKVRgQCz:rk:1:pf:1&frcectupt=true

[GooseJuice]

Thanks guys.  Appreciate the help!

[Spen69]

Dunk the bearings and cages in a cup of petrol and clean them with an old paint brush

Pop them back in, pinch the cages back tight and pack them with grease, job done

Or spend a quid each set for new ones at your LBS if you can't be arsed