Older grease guns had a vent built into the vent plug/screw so that you could opne it a little to let the air out when replacing a grease tube. The newer ones don;t have the vent so you have to completely remove the vent plug/screw. If you take a Dremel cutoff wheel and cut 2 grooves on the vent plug/screw from the bottm to about 2/3 of the way to the head you have the vent. All you do is replace the tube and back the screw out a ways till the air quits then screw the vent plug/screw back in.
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