Caster Mounting - Part 6 - Top Plates

Without a doubt, a top plate is the most common means of mounting a caster. From small to large, light to heavy, top plates provide the most secure and convenient method of mounting. A top plate doesn't need explanation to understand how it works, a plate with holes that one puts bolts through.

With that being said, there is some nuance to getting the right bolt hole pattern. This is critical in replacement applications, the wrong pattern will mean having to return and exchange the caster or having to drill new holes on existing equipment. A typical bolt hole pattern reads as follows:

• 2-5/8" x 3-5/8" slotted to 3" x 3"

This means that the holes on the outside most part of the plate are 2-5/8" x 3-5/8" then slotted to the inner part at 3" x 3". The graphic to the right illustrates this well. Some top plates do not come with slotted holes, others have holes slotted in other directions. Generally speaking, a caster series, with the exception of furniture casters, is defined by its top plate size.

Top plate casters are available in furniture, institutional, industrial and kingpinless types. If you need help finding the right top plate for your application, don't hesitate to contact us.

Caster Mounting - Part 5 - Round Stem

Round stems are by far the simplest stem design around. It is literally a piece of round stock riveted into the kingpin of the caster. They actually are not that different from a grip ring stem. Instead of using a locking ring to hold it in place, it is a simple compression fit.

But, they are very rare. Normally a grip ring or threaded stem is used due to their positive locking. We do not recommend using a round stem, if at all possible. Contact us to discuss your options.

Caster Mounting - Part 4 - Expanding Adapters

Expanding adapters are a hybrid design, utilizing a threaded stem with a flexible socket adapter.  Typically they are constructed with 4 parts: a threaded stem, a compression nut, a rubber expansion ring, and a plastic washer.  In essence, they are a hybrid of a grip ring and threaded stem.  In as much as they do not require special machining of the equipment, but no socket is required. 

Usually these stems are used on equipment where a standard socket is not available because of the inside diameter of the round tube or pipe.  They are installed by inserting the stem into the pipe and then turning the nut on the bottom side of the swivel section to tighten into place.  A pretty simple installation, which also provides for an equally simple removal.

These stems are not indicated for use on equipment subject to large amounts of moisture and heat, such as wash-down or autoclave situations.  This is because the rubber insert can dry-rot.  Once the rubber has dried out the caster may, for lack of a better phrase, fall out of the equipment.  The exposure to moisture hastens the natural decay of the rubber, therefore failure will be premature.  When considering an expanding stem for an application, consider a grip ring or a threaded stem first if the equipment will be in a wet or rough situation, they typically provide a more positive retention mechanism. 

Overall, an expanding adapter provides a flexible alternative to more fixed methods such as grip rings and threaded stems.  Implementing them on equipment can help avoid additional manufacturing or assembly time.  With that in mind, there are some noted limitations, as mentioned previously.  Contact us for help in deciding the correct mounting for your application.

Caster Mounting - Part 3 - Grip Neck (Wood) Stems

A Grip Neck or Wood Stem, as the name implies, is ideal for equipment made of wood. The design and function of the stem is similar to that of a grip ring, however, there are some noted distinctions. They are found only on furniture and institutional casters.

A grip neck stem, as the depicton to the right shows, uses a flanged top to capture the stem in the socket. Generally speaking, a grip neck or wood stem caster requires the use of a pre-manufactured socket, pictured below right.. Though, most commonly used on wood furniture, they are used on certain plastic and metal equipment.

Unlike a grip-ring stem, grip neck stems are available in one size, 5/16" diameter x 1-1/2" long. Given that, they are, by far, the easisest to find replacements for, should they break. As opposed to grip ring or threaded stem where a multitude of similar looking options exist.

There are a few noted disadvantages to using a girp neck stem. First, they are incredibly hard to remove from the socket once installed. Secondly, even though the measurements are the same, sometimes, using a different manufacturer for the stem and socket can cause issues.

A grip neck stem makes an excellent option for wood furniture that needs to be mobile. If you need more information, let us know.

Caster Mounting - Part 2 - Threaded Stems

A threaded stem is quite simple, it's a round piece of metal with a cut thread, as the name implies. The threaded stem is more broadly used, yet less common than the grip ring stem; because threaded stems come in nearly any size, metric or standard, small to large diameter, fine or coarse thread, the options are many. Threaded stems are available standard on institutional and furniture casters, and through special order on industrial casters.

A threaded stem provides a more secure mounting than any other stem mount. Where grip ring and grip neck stems can become loose over time, the threaded stem, short of the stem shearing, will remain in place. A fair comparison between grip and threaded stems is nails to screws.

In order for a threaded stem caster to be attached to equipment, the equipment must have a tapped bore to accept the stem. For the most part adding the tapped bore is part of manufacturing the equipment. However, certain materials, by nature, don't accept a thread very well. In these instances certain adapters are available. Pictured to the right is an adapter for wood, it is installed by drilling a hole to the appropriate outside diameter of the adapter, then the adapter is hammered into place, secured by the webbing off the flange.

Threaded stems, as stated above, are available in nearly any size.  Standard size threaded stems are generally 1/4" to 1/2" coarse.  However, stems as large as 1" in diameter are readily available, although they are special order and can have a slightly longer lead time. 

Noting the disadvantages, installation time is increased as compared to grip style stems. Further, manufacturing time of the equipment may be increased due to the bore and tap requirements.

In summary, the threaded stem provides a near universal method of caster mounting.  The increased manufacturing costs can be a problem, but the secure mounting may offset this.  If you have questions about your application, please don't hesitate to contact us.

Caster Mounting - Part 1 - Grip Ring Stems

The grip ring stem is quite possibly the most common caster stem in use. Used predominately on consumer and commercial office and shop equipment, this stem provides rapid installation and quick change. Grip ring stems are typically available on furniture and institutional casters.

The stem works by utilizing a piece of round steel with a channel machined in the top portion. The machined channel is then fitted with a locking ring, either brass or steel. This ring is slightly larger than the stem itself. The mounting sockets are made to match the stem, with a recessed race in the top portion of the socket, so as to accept the locking ring from the stem. When inserted the locking ring expands into the recessed race, locking the stem into position. The mechanism provides positive retention, without impeding removal should it be required.

Grip ring stems are most commonly used on molded plastic components, wherein the socket can be made an integral part of the equipment. This reduces overall cost and makes for faster manufacturing.

These stems can also be used in equipment made of round or square hollow tube. Pre-sized sockets are available for common mill sizes. Socket inserts are quite inexpensive and provide an easy and simple way to make equipment mobile that otherwise would not be.

There are some noted disadvantages of using a grip ring stem caster. Capacity being the first. Generally speaking, 200-lbs is about the limit of a grip ring stem. This is in part due to the nature of the casters it is sold with, and that it is a narrow distribution of the load. The load being focused on the kingpin entirely. Secondly, over time, it is possible for grip ring stem casters to come loose. So these are not generally indicated for abusive or rough applications.

All in all, the grip ring stem provides a great solution for many mobility applications. Its rapid installation and change-out, high availability, and the variety of casters fitted with grip ring stems, make it a tempting choice for designing a mobile product.

If you have questions regarding your mounting options, please contact us.