The machine I purchased is also a H4. Manual for the 545 lists needle sizes based on models A, B C etc, maximum thread size is not the issue. The Gortex Tenera thread is similar to v-92 thread. They recommend (Tenera) a smaller needle #14, #16 when using the thread.. Pfaff manual says model “c” minimum needle size is #18. Is this based on thread tensioner, needle bar, what?? Model B minimum needle size is listed as a #12.
pfaff 138 sews with the Tenera and sunbrella well, but purchased the 545 for the walking foot, not sure if I have purchased a machine that won’t work with the needle & thread recommendations and the use of the specialty Tenera thread for prolonged outdoor UV exposure.