HC-GBCL Thick Core Boomers Custom Light Electric Guitar Strings (9-48). GUITAR BOOMERS 9-48. Thick Core Boomers are for the players that want more from their strings. A beefier core boosts your playing inspiration by allowing greater sustain, a more focused low end and thicker tone. The thicker core of these Boomers is great for both standard and drop tuning.