Above here is a rough estimate for what I find to be the best string gauges for E13 tuning for a 22.5″ scale instrument. DO NOT OVERTHINK IT. String gauges can have variations usually up or down by a few sizes. If you can find strings roughly around the same size YOU WILL BE FINE. eg. if you have 16 and 18 size string but not a 17 it will be fine. Use what works the strings will stretch. Main goal is to have a reasonable well taught string that is a little on the thicker side to give you a nice round sound. Steel guitar is not like standard guitar. String bending is not used. Some players pull strings but that usually is a technique I avoid now as with 12 strings I get all the voicings I need.
Use the above as merely a guide to get you in the ball park. Some players recommend Nickel strings others who sweat alot recommend stainless steel.
Either way new strings sound bright but keep alot of noise when sliding the bar. Bare with it the more you play them the more smooth “dull” they become. Also we hardly tend to change strings as they usually never break on lap steel unless you have been messing around with tuning it up and down all the time. Its common once my strings become more dull and smooth I leave them on their for 6 months to a year easy. Hope this guide helps you not to panic and just practice and enjoy the journey.
Some old timers used to pour coffee over their strings to get that smooth dull sound and once achieved never change strings. So the key thing is to look for a smooth round tone and adjust your tone knob to make it brighter or more dull. Clean crisp bright sounds tend to feel sharp whereas a warmer rounder more dull sound just blends beautifully and is more pleasant to the ear.
The Lap Steel Guitarist 