If you mean the Sierra click, I do not use the extension and do not shorten the barrel, instead I use the gel refill that need no extension. My bet a customer will loose the extension latest after the second refill change. The type of refill is listed in the instruction sheet. Just yesterday I bought 20 double packs for $1.71 each - not a bad price considered that this pack normally cost around $3. Also, I found that my customers like the gel refill much more than the standard ball point.