Hi,
I would like to ask one question. I am ready to build 7' UL spinning rod mostly for in-line spinners or small spoons. I will use 4lb mono test.
How small can I go for running guides. ( as small as I can).
Thank you for your help!!!

As small as will allow your knots/connections to pass

Mike (Southgate, MI)
If I don't want to, I don't have to and nobody can make me (except my wife) cuz I'm RETIRED!!

If you are not passing knots

This is what I use for
20 braid/ 10mono or floro-- 2mm
6 and 8 lb mono or floro-- 1.5mm

Might could use 10 lb floro with the 1.5's but I've not tried it as of yet

From a practical standpoint, you can use the smallest guides you can get ahold of. Last time I checked, the smallest Batson micro that were readily available were 3.0s. The smallest Fuji that were readily available were 3.5s. Steve can tell you how to get ahold of the 2s and 1.5s, if you want to use those.

You could easily use either 3.5s or 3.0s with 4 lb. line. (Just as a reference, the last micro build I put together used 14 lb. test with Batson 3.0s. It's one of the best rods I've ever put together--it casts and fishes like a dream.)

Make sure to put the micros on a magnet, or in a little cup. They're easy to lose.

on my first micro build I lost two of them, never found them. Then I found how to keep track of them, I trimmed a brightly colored cable tie in width and length so it just fit snugly into the micro, cut its length to about an inch, and handle the micros by hanging onto the cable tie. If I drop it, it's easy to find, but don't drop them nearly as often as before. My next build should be a little cheaper, using just the guides I need for the rod.