Advice on carbide insert boring bar

[PixMan]

I don't see how a 3/8" bar is going to be able to get all the way down to a 1/4" hole.

Minimum bore diameter for most 3/8" bars will be around .410".

With a 3/8" bar you would have to go to the smaller CCxT21.5x size insert anyhow, so consider going to the CPxT1.81.51 size or smaller CPxT1.51.21. The smaller the insert, the smaller the boring bar can be, the smaller the minimum bore.

If it's not more than an inch & half or so deep, I just use Micro 100 solid carbide boring bars. They rock!