BMX - SeatPost /Clamp Confusion

A while back i started buiding a 20" Bike... half show/half freestyling

So far i have bought:

Frame
Handle Bar
HeadSeat
Stem
Fork


But im now having problems with the seatpost/clamps

I didnt knew there were so many #$&@ different sizes in seatposts...

I wanted a Layback seatpost with support, so i went to ebay since you dont see those around anymore, i manage to find a new one and bought it, but when i got it it happens that is to thin for my frame..

The size of the one i bought is a 22.2mm, well i walked to the garage and took the seatpost of my nephews bike to test it out on my bike, its alot thicker than the one i bought except there is still a little bitty space, meaning i didnt had to force the seatpost in, is it suppose to be like that? or im suppose to be able to force it a bit to put it in?

My nephews seatpost is a 25.4mm...is that the size i need? or i need a 26.8 or is that to thick?

The frame i got is a 2000 GT/DYNO

All this s*** is giving me a headache >_< , back in the days when i was like 15, when we use to build bikes i didnt remember having trouble with seatpost -_-


Also, my nephews seatclamp didnt wanna fit on my frame...

then again his bike is a 16" i think....

thanks alot

if the seatpost you bout is to skinny go to your local bike shop and talk to them about a seatpost shim. nowadays most bikes have 25.4 or dk i think has a 26.4

Yeah i thought bout getting that but...i think i rather get the right seatpost, i just finished putting that seatpost for sale on ebay...i hope $11 is not to much asking.

So 25.4 is what i need im guessing? and a 1" seat clamp right?

You use a 1-1/8" clamp with a 1" (25.4mm) post.

You need to measure the seat tube to find out what size clamp you need. Seat posts come in a heap of sizes, and using a shim is no big deal. Measure twice, pay once.

Thanks alot for all the info guys, i appreciate it.