Use the stringing range for your exact weight variant. Choose string thickness and tension as separate setup decisions.
Use the correct range
The selected Astrox 77 Play, 99 Game and 99 Pro 4U versions list 20–28 lb. Nanoflare 001 Clear 5U lists 20–27 lb. The 99 Pro 3U version lists 21–29 lb, so its limit must not be applied to the 4U version.
String thickness is another variable
Compare the same string model and thickness before changing tension. A thinner string generally gives up some abrasion and breakage resistance relative to a thicker version, but construction and use also matter. Do not assign a fixed number of playing hours from thickness alone.
Record the setup
Write down the racket version, string model, thickness, reference tension, machine and date. If you measure tension later, use the same device and method.
Inspect wear before playing
Check for fraying, broken grommets and frame damage. Ask the stringer to inspect damaged parts before restringing. Keep the racket away from prolonged heat, and replace a damaged string setup according to its condition rather than a universal hour count.