Bolster No Inserts RPM Neck Bearing Diameter. 1 HF 1 15000-18000 6.80 mm 2 HF 21 12000-15000 7.80 mm 3 HF 2C 8000-12000 7.80 mm 4 HF 3C 8000-12000 8.80 mm 5 HF 44 8000-10000 10.00 mm 6 HF 55 8000-10000 12.00 mm 7 HF 66 - 14.00 mm 8 HF 68 - 14.00 mm 9 HF 77 - 16.00 mm Heavy Duty Bolster Standard or special design with various flange and brake designs possible according to customers drawing or sample. Tire cord spindle with type (HF) HZ55, HZ68, SMM-32, SMM-42 of SKF and other manufacturers Draw-twister spindle with type (HF) HZ55, HZ68, HZ77, SMM-32, SMM-42, SMM-52 of SKF and other manufacturers The design of the spindle bolsters of the HF series - i.e. HZ44, HZ55, HZ66, HZ68 and HZ77 - corresponds to that of well-proven spindle bolster, millions of which have been used by the textile industry. However, owing to most modern manufacturing methods, they were optimized to a degree unknown up to now. The result is:» Low vibration » Low power consumption » Low noise level » Low maintenance costs » Less out of balance wear on neck bearing The result is: » Low vibration » Low power consumption » Low noise level » Low maintenance costs » Less out of balance wear on neck bearing