I purchased some Fuji Ultra Poly Size D thread and it seems to me the D thread is not as thick as others. I was just wondering if Fuji thread is just a little thinner then other size D thread. Used it on a 15/30lb Rainshadow Rod with Alps guides. Use a single wrap of thread on the guides and I am hoping it is a strong wrap. Thanks for your help, and Have Great New Years

Dennis,
You can put the thread in a strain gauge and determine its breaking strength.


Then you can put other size D thread in the same strain gauge to determine their breaking strength.

Or, you can just use a spring scale. Take a length of thread, and tie a double overhand loop in each end. Then, use the scale to see where samples of each type of thread breaks.

Take care

It’s plenty strong enough.
Norm

Not sure about what it's diameter is since Fuji doesn't list it's diameter on the individual spools. Diameter is what equates to "Thickness" but testing at what point the thread routinely breaks out when subjected to extreme stress won't give you definitive results on whether it's thicker or thinner than other manufacturers D threads .

A "D" size thread from one manufacturer may have a higher breaking average than a different manufacturers "D" size thread and that would give an indication that it may indeed be thicker but it's not proof of one thread having a larger diameter than another. I personally would not be concerned because i actually would prefer the thinner thread and use Size A for everything with no issues.

Fuji Poly thread is very good thread , i like it and most others seem to as well .

I have 30+ year old rod built with no underwraps on "A" thread still going strong on a diet of 6 ft.+ sturgeon and sinkers between 1 & 3 lbs, in heavy current, you'll be fine.

There are many who are overly concerned with the (breaking) strength of wrapping thread to keep the guides in place. The concern is unwarranted when logically examining the application and function of even size A thread to wrap a guide.
The size A ProWrap I use withstands more than 2.5lbs of force before it breaks; let’s allow a 20% + margin of error and say its breaking strength is 2lb. Wrapped on the blank, size A is about .009in wide. Next, multiply the number of threads required to cover the foot (feet) of the guide; given the same ring size, the foot a single-foot guide is approximately twice that of a double-foot = the number of total wraps is roughly the same. The foot of a KL-H10 is .625in long. So, .625 / .009 = 69.44 or 70 wraps. Now, multiply the number of wraps times 2lb; 70 X 2lb = 140lb. That means there is 140lb of force holding that guide in place.
If anyone is still in question, let’s look at it from a different perspective = how much force can a typical fishing situation place on a guide? I will use an off-shore tuna rod sporting six guides as an example with a monstrous 50lb of applied drag. Remember, we are not dead-lifting this 200lb tuna into the boat. Admittedly, when the rod bends, each guide will carry a different amount of the total force, but for ease of explanation, let’s assume all guides carry an equal amount of force. So, we will divide the total amount of force by the number of guides; 50lb / 6 guides = 8.333lb per each guide. The amount of force applied to each guide is actually less due to the shallow angle of the line rather trying to pull it straight off at a 90* angle. For laughs and giggles, let’s hypothetically dead-lift that 200lb tuna into the boat; 200lb / 6 guides = 33.33lb per each guide.
When comparing / combining the two perspectives, it should be obvious that it is virtually impossible to apply enough force to a rod while fighting a fish to break the thread wraps, even size A. Although, being larger in diameter, size D is stronger, there will be a fewer number of wraps within the same length and may not add considerably to the overall strength of the wrap. To be fair, the threads closest to the guide legs will be stressed more than those at the tip of the foot.
Basically, I wrap freshwater rods with size A, saltwater rods with D and rods over 40lb I under-wrap with size A. However, I fail to see the point of double over-wraps; I would hope and expect anyone purchasing a rod from me would avoid kicking and banging it around to require additional threads to be nicked and scraped. But if a customer wants a double over-wrap, who am I to argue?

Mark Talmo
FISHING IS NOT AN ESCAPE FROM LIFE BUT RATHER A DEEPER IMMERSION INTO IT!!! BUILDING YOUR OWN SIMPLY ENHANCES THE EXPERIENCE.

Unless the rod is a spinning or spiral wrapped the blank is taking the load. Not the thread.

Freddwhy (Rapt-Ryte)