Retention knobs and pull studs are indispensable in keeping your metal parts firmly in place while you work on them. To the untrained or novice eye, many retention knobs and pull studs look identical. They are not, but it can be very difficult to tell just from eyeballing them — you must check the size printed on the retention knob or pull stud. Because they look so similar, without adequate attention to detail, you may use the wrong retention knob or pull stud in your machine. Especially common is mistaking a metric-sized knob or stud for an imperial (standard) knob. The machine may appear to operate correctly when such a mistake is made, but the danger of failure or breakdown — and injury — is increased. Therefore, our industrial tool supply company recommends that customers who are the least bit uncertain about which knobs or studs to purchase consult with our staff over the phone first. At this time, we can give you our expert professional advice. We also recommend you keep your retention knobs and pull studs in an organizer that denotes which size is which, to cut down on confusion. Also remember to clean them periodically in a parts washer.