thanks guys. I took the bike in to the store that pulled my bottom bracket and headset.
Which measurement is most critical? Seatpost tubing diameter or the DIY shim's diameter? (Remember: Ther was no original seatpost fitted to this bike when I got it other than the DIY shim.) Do bike component specs, such as seatpost diameter, vary depending on which region the bike is sold in (Europe, US, Asia-Pacific)?
ok, took it to the bike shop (who have already done some work on my bike). They were kind enough to measure it with a pair of (non-digital) calipers. They measured the DIY shim's diameter, since that's what the previous owner used as a seatpost shim (nearly 1' long). Here's where it gets weird: calipers measured 30mm. But both guys shook their head (this is Europe) in disbelief, and concurred on the correct diameter being 29.8mm; not 30mm, as the DIY shim's diameter measured. What do you guys make of this?
I'm under the impression that this bike (Giant Boulder Alu Lite 6061) was mostly distributed in Europe and the UK. Most of my searches indicate that the only people that sell them used hail from either the Benelux countries or the UK. I haven't found anyone in the US selling them used (is this relevant?). Could this fact somehow correlate to the diameter? I came across several threads that indicated there is such a thing as 30mm seatpost diameter. One of the mechanics seems pretty old school, so I'm guessing he's clever enough to recognize the likelihood of a 30mm DIY seatpost actually being a shim for a 29.8 hole. I don't know.... It looks like the bike dates from the mid-90s, there's a possibility the frame's seatpost tubing expanded over a 20-year lifetime - isn't there?
Again - thanks for all the input.