Here's a visual guide to all the yellow hardhats worn by the four GB's in Ghostbusters 2.
In the street scene, shot in LA, Aykroyd wears an Eastern Safety Tuf-E, Ramis wears a Jackson Safety Sentry. (ID'd by ramcuda.) Murray wears an as-yet-unidentified hardhat with a vaguely spade-shaped flat area above the bill. Only Aykroyd's Tuf-E sports a JustRite headlamp in this scene, while Murray and Ramis' hardhats sport various stickers.
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When Aykroyd is lowered into the shaft, shot on a soundstage, his Tuf-E changes to a different lamped hardhat and back-- TWICE!
On this fourth style of hardhat, note the single low ridge down the middle and the somewhat triangular boxy areas above the temples.
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Later in the film, when all the GB's except Murray go into the subway tunnels, both Aykroyd and Ramis wear Tuf-E's with headlamps. Hudson wears a fifth style of hardhat, also with a headlamp.
The details of this hardhat are almost backwards from those of a Jackson Safety Sentry. Note the pointed stripe on the back of the ridge, very similar to the front of Egon's hardhat from the earlier street scene.
Another tiny continuity error... for one brief shot during the severed head scene, Winston's hardhat is missing entirely.
The train tunnel scene was the last scene shot using the hardhats, during reshoots done months after principal photography. It was filmed in a NYC nightclub that contained old subway tracks.
Note the amount of yellow paint that has flaked off of the two Tuf-E's, both of which were originally white.
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The next scene edited, back on the Van Horne soundstage set, was actually shot much earlier.
Egon is still in a Tuf-E, but now Winston and Ray are both wearing 'number four style' hardhats with the single ridge down the middle. Egon's Tuf-E in this scene shows no damage to the yellow paint job.
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So, by my count, assuming that Ray and Egon are simply swapping two Tuf-E's around to account for the different wire placements, there are a minimum of seven hard hats in all.
Venkman's with the 'No Bozos' and '100%' stickers
Egon's Jackson Safety Sentry with 'Runway Visual Range' and other stickers
Ray's Tuf-E with JustRite headlamp
Ray's alternate single-spine with headlamp
Winston's train tunnel hardhat with headlmap
Egon's Tuf-E with headlamp
Winston's alternate single-spine with headlamp
Alex