This is a device attached to an explosive weapon to increase its fragmentation effects. Modern battlefield weapons such as rockets, missiles and grenades have been increasingly optimized to destroy hardened point targets (tanks) rather than provide effectiveness against softer targets (such as trucks or people) over a wide range. As a result, many if not most of the precision-guided weapons available in the field presently have a limited effect against softer grouped targets. One means of improving their effectiveness without designing new weapons is the fragmentation sleeve.
Such a device can be either a purpose-built rigid applique, intended to be installed on the weapon by depot handlers (in the case of expensive missiles) or it can be a simple item intended for use by the weapon's user - infantry, in the case of most smaller weapons.
On the high end, the U.S. AGM-114 Hellfire "Mod K" carries a rigid device intended to encase the warhead of the Hellfire and provide additional fragments on detonation.
On the low end, as far back as World War I, the German army used distinctive "stick" grenades (Model 24, 43 Stielhandgranate or potato mashers). These were thin-skinned and relied mostly on blast; however, this made them less effective (shorter lethal radius). As a result, the Germans produced the Splitterring, a fragmentation sleeve consisting of pre-scored steel which slipped around the grenade. Two-part egg-shaped versions were also produced for ovoid grenades (Eihandgranate 39). Even in modern times, there are designs as simple as elastic sleeves with glued-on shrapnel intended to improve hand-carried weapons.