| Business | Phone |
| Associated Engineering Co 2917 Martin Luther King Jr Pky, Des Moines 50310 | (515) 255-3156 |
| Oakes Engineering Co 949 65th St, Des Moines 50312 | (515) 255-1777 |
| Pelds Engineering Co 2323 Dixon St, Des Moines 50316 | (515) 265-8196 |
| Dale M Smith Technical Svc Po Box 67, Des Moines 50301 | (515) 283-0069 |