ZilchPlugz™ are merely plumbers' test plugs from the hardware store. They come in various sizes and expand with a thumbnut to seal the end of a drain pipe or speaker port. $3 - $5 apiece, depending upon size and type.
JBL woofer gaps are narrow, but it's rare that a skilled refoamer has to use shims to get the voice coils into a satisfactory alignment....
JBL woofer gaps are narrow, but it's rare that a skilled refoamer has to use shims to get the voice coils into a satisfactory alignment....