2029-x-SMLF Series GDT Surge Arrestors Bourns 2029-xx-SMLF Series GDT Surge Arrestors are heavy duty 2-electrode Gas Discharge Tube (GDT) arrestors in an 8mm x 6mm surface mount (SM) package. This series is Class 5 rated and attains the highest performance classification available under ITU K.12 requirements. High performance in a compact surface mount package makes this Bourns series ideal for use in heavily exposed telecommunications, commercial, and industrial applications.