I build a lot of spinning rods for myself, family and friends. Moslty 6'6" & 7' medium to med-light, fast action (6 - 12) line for bass.

I used to always use size "A" thread for wrapping guides until the finish on the guide feet (single foot guides) started cracking at the end of the foot. This occurred mostly on the first and second guides up from the reel (#30, #25 or 20 sizes).

So I started using size "D' thread on alll guides a few years back and it eliminated this cracking (except after a few years of use I see some on my rods).
I do prep my guide feet well, similar to pictures shown on posts here and down to a "knife edge".
I use high build flex coat with no CP, usually (2) coats.

What caused the cracking and why did the "D" size cure my problems?
Does it hold the guides tighter? Allow for a thicker overall finish?

I'm looking to start building with the smaller micro style guides and would most likely have to switch back to "A" for those for overall weight reduction. I know I should use "A" for all guides but I don't want this problem to reoccur.

The D thread didn't really cure anything other than making the cracking harder to see. It may reduce this problem a little, but it won't eliminate it. A stiff guide foot on a flexible rod blank causes the cracking as the guide resists the blank's attempt to flex it under the clamp of the thread. The thread is the weak link in the chain and when it stretches a small crack or check will appear in the finish. This is more common on the more highly flexible portions of the rod than on areas where there is less flex.

There are really only 2 things you can do in order to reduce the tendency of the finish to crack. First, is to grind the guide foot to a very shallow taper which makes it a tad more flexible. The second thing, and one which you can't always do, is to wrap with a great deal more tension which clamps the guide foot tighter to the rod blank, preventing any movement or lifting of the guide. But that much tension isn't good for the rod blank.

...........

I have found that using size D thread on heavy offshore rods will actually make the cracking worse. I have switched up and gone to 3 layers of "A" thread for better finish perfusion.

Kevin

Steven,
You say that the cracking is occurring at the end of the guide foot.
Which end of the foot. i.e. the ring end of the foot, or the non ring end of the foot.

If it is at the ring end of the foot, you might add a locking wrap to your guide to further stabilize the guide at that end.

Or, if it is at the non ring end of the foot, do as Tom suggested, and thin the entire length of the foot - with a sander or grinder to make the foot more flexible.

Remember, you are only trying to hold about 10 lbs of pressure, so that there is no need for a very thick foot on the guides. Just use common sense if you do this to not weaken it too much.

If you decide to go this route, take some old guides and try thinning the guides to various amounts and check their bending and breaking strength.

Take care
Roger