There are three different options: 

•  4 high blow bar , normally used to used to crush material -250mm, end product -10mm;
•  3 high blow bar, used to product more fine end product;
•  2 high and 2 low,  the most commonly used configuration. 

Wear life of blow bar affect by many factors:

• About 45% for material
• About 10% for moisture of material
• About 8% for the crushing ratio rate
• About 10% for the fine content of raw material
• About 20% for the speed of the rotor
• About 10% for opening size of the first and secondary impacting bar 

Based on the different abrasive content of the raw material, choose different blow bar for Reducing the cost of wear parts.

There are Manganese, Martensitic, Martensitic/Ceramic,Medium Chrome, High Chrome, toughened Chrome, High Chrome/Ceramic for your choice. 

Below is the a reference between abrasive resistance and toughness. 

For more detailed suggestion, pls kindly contact with us for further analysis.