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The ''hump filler'' is basically a variation on the theme of the [[crescent filler]] in which the sac is compressed using a protruding element from a side opening of the pen. The element allows you to compress directly the rubber sac, the main differences between the variants of this filling system are the ways in which it ensures, more or less reliably, that the protrusion can not be pressed accidentally.

<noinclude>{{ReferBox|Filling systems}}</noinclude>The ''hump filler'' is basically a variation on the theme of the [[crescent filler]] in which the sac is compressed using a protruding element from a side opening of the pen. The element allows you to compress directly the rubber sac, the main differences between the variants of this filling system are the ways in which it ensures, more or less reliably, that the protrusion can not be pressed accidentally.