Getting Started with Guitar Slides - Part 1 - Length

LENGTH

Your slide needs to be of sufficient length to bridge all the strings you wish to bridge.  On a three-string guitar, I find a 4.7-cm slide manageable but bordering on too short.  The neighborhood of 6-7 cm seems about right to me.  (Prominent cigar box guitar player and YouTube-ist Shane Speal strongly advocates a shorter, or "stubby," slide.  So even regarding length there can be scope for preference.)