All came in as expected

In order to achieve maximum design load capacity, the taper of the machine screw head must match the countersink angle of the track hole, i.e., full surface area contact between the fastener and track.

The countersink angle of the track hole is 120 deg, both per the manufacturer's spec on the item page and from my validation measurements. This necessitates a head taper of 120 deg. Unfortunately, a 120 deg tapered machine screw does not exist.

The spec US Cargo Control fasteners listed here claim to have a head taper of 90 deg, not 120 deg (which again, doesn't actually exist). Not only that, but a 90 degree head taper is the standard taper for metric, while the standard for imperial is 82 deg. This leads me to believe these fasteners have an actual taper of 82 deg because 1/4-20 90 deg taper machine screws also don't exist. Specialty fasteners with a 100 deg taper are available in imperial sizing, but usually in limited lengths.

So, in conclusion, first you cannot achieve the max design load for this USCC L-Track because a 120 deg tapered machine screw doesn't exist. Second, if you want to achieve the highest possible load rating, understanding that a 120 deg machine screw doesn't exist, and these are likely 82 deg tapered, go to McMaster Carr and purchase some 1/4-20 100 deg tapered machine screws to your preferred length.

Hardware was as advertised but not what I needed. The L track has a 100deg countersink while these bolts are 90deg. I don’t understand they sell hardware that doesn’t match the L Track.

Didn't realize the 72" rails have 15 holes per side as only purchased one package of nuts and bolts which included flat washers only. Luckily my local Ace hardware had the exact same ss bolts and lock washers which I used when installing.

A little outrageous that these are not already included with the L-track. Each 8' section requires 25 screws, so plan to add $30 to the cost of each strip to attach it. As others have said, the countersink angle is atypical(100 degree), but can be found on mcmaster carr's website under Mil. Spec Stainless Steel Flathead Screws. This will allow you to get the length you need. Pricing ends up about a wash, so if you can work with 1.5" bolts, ordering them here is just fine.