This front-mounted shutter system uses the time-proven, reliable Packard-Ideal pneumatic shutter installed on a compact high density panel mount. Two Packard types are available; the #5 is the basic manually timed unit. The shutter remains open as long as the bulb is squeezed. A quick squeeze and release is about 1/10th second exposure.
Packard Shutters
 
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Cokin Mount
Collar Mount
3-1/2” diameter shutters...http://www.youtube.com/watch?v=JXc2E94_aMw&feature=youtu.be
3” diameter shutters...http://www.youtube.com/watch?v=9uqQmzlRMRI
Factory New Packard...
The #6 Packard features two modes: Inserting a special pin yields a consistent 1/25th second exposure with a single firm squeeze of the bulb. Removing the pin reverts the shutter to the #5 mode (fully manual timing). The pin is precision ground tool steel, using a common nail may result in erratic and imprecise operation of the shutter. Do not insert the pin while the shutter is open; damage to the blades may result. Do not use a lubricant.
                            See the #6 Packard in operation Here...
 
See this shutter...See this shutter...