Hasler IM-460 User Manual page 39

Do not try to seal self-adhesive envelopes.
Close them before feeding.
Thickness setting:
For thin or thick envelopes, you may have to adjust the thickness
setting of the feeder. Use this setting if several thin envelopes
pass at a time in the feeder or, on the contrary, if thick envelopes
are blocked at the entrance of the mail path.
1
Open feeder cover.
2
Change lever position:
1 for thin envelopes
2 for thick envelopes.
3
Close feeder cover.
3
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