How to Choose a Clock Mechanism: Shaft, Hands and Torque

To choose a quartz clock mechanism, check four things in this order: the shaft length against the dial thickness, whether the hands will fit the shafts, whether you want a step or sweep seconds action, and whether the movement has enough torque for the hands. Get these four right and the replacement works the first time. Get one wrong and you get hands that sit crooked, rub the dial or stall.

This guide is for jewellers, clock repairers and retailers who fit replacement movements for customers. You can browse the range in our watch and clock spares catalogue.

Step 1: Measure the dial thickness to get the shaft length

The threaded neck at the front of the movement passes through the dial or clock face and is held by a nut. If the neck is the wrong length, the rest of the fit goes wrong. This is the most common reason a replacement movement is returned.

1. Measure the thickness of the dial or panel at the centre hole. Use callipers if you have them. Wood, MDF, glass and metal faces vary a lot.
2. Add anything that sits between the movement and the front of the dial, such as a recess, a spacer, a second panel or a thick washer.
3. Add the nut and washer allowance, so that the nut can fully grip the thread.
4. Compare the total with the movement's usable thread length. Suppliers describe this in different ways, so look at the maker's specification rather than the overall body size.

If the neck is too short, the nut will not bite properly and the hands will sit too low. If it is too long, the hands stand proud of the dial and look wrong from the side. Movements are made in several shaft lengths for this reason, and thick wooden or layered faces usually need a longer shaft than a thin printed dial.

Tip: if you are replacing an existing movement, keep the old one next to the new one and compare the threaded neck directly. Do not assume that two movements that look alike have the same shaft length.

Step 2: Check that the hands will fit the mechanism

The movement has three concentric spindles: a hollow hour pipe, a minute shaft, and a seconds post on movements that drive a second hand. The hands must suit them. Hands are normally fitted in this order:

1. The hour hand goes on first. It pushes onto the hour pipe.
2. The minute hand goes on the minute shaft and is held with the small nut.
3. The second hand, if there is one, pushes onto the seconds post last.

Most problems here come from mixing hands and movements that were not made for each other. Check the hand hole shape and size against the shaft, and check that the stack of hands leaves enough clearance between the hour hand and the dial, and between the minute and hour hands.

If you sell a clock mechanism kit, where the movement comes with matching hands, the fit question is mostly solved. Where you buy movements and clock hands separately, check both against each other before you sell them as a pair.

Step 3: Sweep or step seconds movement?

The two types differ in how the second hand moves.

Step is the usual choice when the customer wants the clock to behave as it did before. Sweep is the usual request when the tick is the problem. Sweep movements are often described as using batteries a little faster, so check the maker's information if battery life matters to your customer. If the clock has no second hand at all, you can still fit either type and simply leave the seconds post bare.

Step 4: Match the torque to the size and weight of the hands

Torque is the turning force the movement can deliver. A standard movement is designed to move hands up to a stated length and weight. Long or heavy hands put extra load on the motor, especially in the upper left of the dial where the minute hand is lifting its own weight.

A movement with too little torque will often:

• stall or slow down on the way up, often around the 9 o'clock position
• lose time, then stop
• seem fine on the bench lying flat, then fail once hung on the wall

For large wall clocks, use a high-torque movement and check the maker's maximum hand length. Material matters as much as length: aluminium hands are light, while wood, brass and thick metal hands are heavy. When you are close to the limit, move up a torque class rather than hope for the best. A hand that is slightly counterbalanced behind the pivot also eases the load.

Other things to check before you order

• Pendulum or plain: pendulum movements have a drive for a swinging pendulum. They are not interchangeable with a plain movement.
• Chime or strike: if the original clock chimed, you need a movement that does the same.
• Hanging method: check how the movement mounts, and whether the case or dial recess leaves room for its body and battery holder.
• Battery: most quartz clock movements use a standard cell in a holder at the back. Confirm the type on the maker's specification.

Quartz movements are a different job from mechanical, weight-driven grandfather clock movements. Those are usually matched to the clock's case, dial and weights, so identify the existing movement carefully before ordering a replacement.

A quick selection checklist

1. Measure dial thickness and total mounting depth, then pick the shaft length.
2. Confirm the hand type and hole fit for the hour, minute and second hands.
3. Choose step or sweep.
4. Check the hand length and weight against the torque rating.
5. Confirm pendulum, chime or plain, and that the body fits the case.

Frequently asked questions

What is a clock mechanism?

A clock mechanism, also called a clock movement, is the motor and gear train that turns the hands. In most modern wall and table clocks it is a battery-powered quartz unit that is fitted behind the dial.

How do I know what size clock mechanism I need?

Start with the shaft length, which depends on the dial thickness, then match the hands and torque. The overall size of the clock or dial matters mainly because it decides how long and heavy the hands are.

Can I use a standard mechanism on a large wall clock?

Only if the hands are within the movement's rated length and weight. Larger wall clocks generally need a high-torque movement, and it is worth checking the rating before you fit one.

Where can I buy clock movements for sale in bulk?

SM Watch Wholesale supplies clock movements and dials to the trade, including jewellers, repairers and retailers. We do not sell to the public, and trade customers sign in to see prices.

Can I use any clock hands with any mechanism?

No. Hands must suit the hour pipe and minute shaft of the movement, and long hands must be within its torque rating. Check both before you sell them together.

Next step

If you are stocking up on replacement movements for your bench or shop, have a look at the spares catalogue. We are a trade wholesaler at No. 9 Bazaar Street, Marabastad, Pretoria, and you can read more about us or check delivery and collection options before you order.