What is a pay item?
A pay item is a single line of work that gets billed by the unit: a description, a unit such as foot, each, square foot or hour, and a quantity. You are paid the unit price times the quantity you actually install, so the count in the field is what decides the check.
There are two ways to price a job. Lump sum is one number for the whole thing, and you carry the risk if it takes more than you thought. Unit price breaks the job into pay items, each with a rate per unit, and you are paid for the quantity you actually build. Underground work leans on unit price because nobody can honestly count from the surface how many feet of rock a bore will hit.
What a pay item looks like
Three parts, and only three: what the work is, the unit it is measured in, and the quantity. Placing cable in a bore is measured by the foot. Setting a handhole is measured each. Restoring asphalt is measured by the square foot. The rate lives on your side of the paper; the pay item itself is just the work and its unit, which is why a list of pay items with quantities, and no rates, is a document you can share.
Why the count is everything
On a unit-price job the field number is the money. Bill four hundred feet you did not build and it comes back on the next audit; build them and fail to record them and you worked for free. That is why production gets tracked item by item as it happens, footage and structures and splices, and reconciled against the scope before a pay application goes out.
Pay item, scope, bid
The three fit together. The scope of work is the list of pay items with their quantities and no prices. The bid is that same list with your rates applied. The pay application is that list again, with the quantities you actually installed. Keep them in the same order and the same wording and they line up item for item, which is the whole point. The fiber scope sheet builder starts you from a catalog of standard work items so the list reads the same all the way through.