Spring-loaded Replicator 1 Drive Block
by Thingiverse
This is an derivation of the "Spring-loaded Replicator 2 Drive Block" by MakerBot to make it compatible with the Replicator 1 (single and dual extruder). Only minor changes has been made, as outlined in the list below. Based on the work of Thingiverse users MakerBot, whpthomas, emmett and whosawhatsis.
It is the same spring-loaded arm used to squeeze the filament between the drive gear and a bearing with a constant amount of pressure. Minimizing the chance of skips due to variance in filament thickness. Both normal and mirrored models are available to fit either side of the carriage. The models are offered as STL and STEP files.
A simple spring height adjustment part is included to easily increase the spring rate if needed. This piece fits over the stub on the base part.

Cut upper-left corner wall from the lever to fit the Replicator 1 extruder mount carriage
Changed the lever and base screw hole to accept a regular countersunk M3 hex screw (easy to find find)
Cut a slight piece off the cover to avoid resting on the drive gear
Decrease the bearing bolt stub diameter to fit the readily available 623ZZ bearing (3 mm vs. 4 mm ID)