Spare parts behave differently from sales stock. Demand is irregular, a single missing bearing can stop a production line, and some parts move once in three years but cost days of downtime when they are not there. At the same time, storerooms fill up with parts for machines that were sold years ago.
This guide explains how to classify spares, set min, max and reorder points, and works through a spares list for a production line. It then covers storeroom controls, common mistakes and an FAQ.
Which spare parts should you keep in stock?
Start by scoring each part on two questions: what happens if it is not available when needed, and how long it takes to get. Many maintenance teams use a simple criticality scale, often called VED: vital (stops production or creates a safety risk), essential (degrades output) and desirable (can wait).
Combining criticality with usage gives four groups, each with its own stocking rule:
| Group | Typical parts | Usage | Stocking rule |
|---|---|---|---|
| Insurance spares | Gearbox, main motor, PLC card, compressor | Rare, maybe once in several years | Keep one, regardless of movement. Review yearly, not by turnover |
| Critical consumables | Bearings, seals, belts and sensors for key machines | Regular | Min/max with safety stock based on lead time |
| Routine consumables | Filters, lubricants, fuses, fasteners | Regular and predictable | Min/max with low safety stock, or a supplier-managed stock agreement |
| Non-critical slow movers | Parts for low-criticality equipment | Rare | Do not stock. Buy when needed |
Lead time changes the picture in the Gulf. Many machine parts are imported from Europe or Asia, so a part that is a two-day local purchase in one country can be a six-week shipment here. A part that is "essential" with a six-week lead time is often treated as vital for stocking purposes.
Insurance spares need a different conversation with finance. They look like dead stock in a turnover report, but the cost of a week of lost production usually far exceeds their value. Flag them as insurance items so they are excluded from slow-moving stock reviews.
How do you set min, max and reorder points for spares?
For parts with regular usage, three numbers do most of the work:
| Number | Formula | Meaning |
|---|---|---|
| Safety stock | (Highest monthly usage × longest lead time) − (average monthly usage × average lead time) | Cover for a busy month or a late shipment |
| Reorder point (min) | Average monthly usage × average lead time in months + safety stock | When stock falls to this level, order |
| Maximum | Reorder point + order quantity | The ceiling, so repeated orders do not pile up |
The order quantity is usually set by practical limits: supplier pack sizes, minimum order values and shelf space. For cheap consumables, ordering three to six months' usage at a time is often sensible; for expensive parts, order closer to the minimum.
Two adjustments make spares planning more accurate than a simple average.
Add planned demand from the maintenance schedule. If the preventive schedule says six forklift services next month, each needing one oil filter, those six filters are known demand. Reserve them against the work orders and reorder ahead of time, rather than waiting for stock to fall.
Use history carefully. Usage from the last 12 months includes breakdowns that may not repeat, and misses ones that will. Recalculate min and max every six months, and after any big change, such as adding a machine or switching suppliers.
For insurance spares, the formula does not apply. The minimum is one, the maximum is one, and the reorder point is the moment the part is used.
What does a spares list look like? A worked example
A bottling plant in Dubai Industrial City reviews the spares for its main filling line. Lead times are in months; usage is per month.
| Part | Group | Avg usage | Highest usage | Lead time (avg / longest) | Safety stock | Min | Max | Unit cost (AED) |
|---|---|---|---|---|---|---|---|---|
| Filler valve seal kit | Critical consumable | 8 | 12 | 1 / 1.5 | 10 | 18 | 42 | 150 |
| Conveyor drive belt | Critical consumable | 2 | 4 | 0.5 / 1 | 3 | 4 | 10 | 220 |
| Hydraulic oil, 20 L | Routine consumable | 3 | 5 | 0.25 / 0.5 | 2 | 3 | 9 | 260 |
| Capper gearbox | Insurance spare | Rare | — | 2.5 (about 10 weeks) | — | 1 | 1 | 28,000 |
| Roller for old labeller | Obsolete | None in 26 months | — | — | — | 0 | 0 | 90 |
For the seal kit: safety stock is (12 × 1.5) − (8 × 1) = 10. The minimum is 8 × 1 + 10 = 18. The plant orders three months' usage, 24 kits, so the maximum is 42.
The review produced three decisions:
- Buy the capper gearbox. It had never been stocked because it had never failed. The line contributes about AED 25,000 a day, so a 10-week wait for a replacement would cost far more than the AED 28,000 part. It is flagged as an insurance spare.
- Write off the labeller rollers. The 14 rollers, worth AED 1,260, fit a machine sold two years ago. Removing them frees a shelf and cleans up the stock valuation.
- Link seal kits to the preventive schedule. Each 500-hour filler service uses two kits, so planned services now reserve kits automatically, and the buyer sees demand weeks ahead.
At maximum levels, the four active parts hold about AED 38,840 of stock, most of it in one gearbox that protects the whole line.
Which storeroom controls keep spares accurate?
Min and max levels are only as good as the stock figure they are checked against. Most spare-part stock errors come from parts leaving the storeroom without a record.
Issue every part against a work order. The storekeeper should not hand out a part without a work order number. This gives an accurate stock figure, and it also builds the cost history for each asset, so you can see which machine eats seal kits.
Record returns. Technicians often take two parts and use one. If the second goes back to the shelf without a return entry, the system thinks it is gone, the buyer reorders, and stock builds up.
Give each part one item code. The same bearing is often bought under the manufacturer's part number, the machine supplier's number and a local description. Merge them into one code with the alternates listed, or the storeroom holds three stocks of one part.
Count critical spares more often. A monthly count of vital parts and a yearly count of the rest catches problems while they are small.
Review slow and obsolete stock once a year. List parts with no movement for 24 months, check them against the current asset register, and dispose of parts for equipment that has gone. Keep insurance spares out of this review.
Repairable parts need their own status. Motors and pumps sent out for rewinding or repair are still assets. Track them as "under repair" with the vendor, so they are not forgotten or reordered.
What are the most common spare parts mistakes?
| Mistake | Effect | Fix |
|---|---|---|
| One stocking rule for all parts | Insurance spares missing, cheap consumables overstocked | Classify by criticality and usage, with a rule per group |
| Min/max set once and never reviewed | Levels drift away from real usage | Recalculate every six months and after equipment changes |
| Parts issued without a work order | Stock figures wrong; no cost per asset | No work order, no issue |
| Duplicate item codes | Same part stocked several times, or reordered while on the shelf | One code per part, with alternate part numbers listed |
| Insurance spares written off as slow-moving | The one part that protects the line is gone when needed | Flag them and exclude them from obsolescence reviews |
| Lead times taken from the supplier quote | Real lead times, including shipping and customs, are longer | Use actual receipt dates from past purchase orders |
Checklist for a spare parts review
What does HYP see in maintenance storerooms?
In plants and facility operations across the Gulf, our implementation team often finds that the maintenance storeroom is the least accurate stock in the business. Sales stock is counted because finance watches it; spares are counted once a year, and the count rarely matches. Parts are issued on verbal requests, and the same bearing sits under three codes.
When the storeroom is brought into the system, the first stock count typically finds two problems at once: parts the system says exist but are gone, and parts on the shelves that the system has never heard of. Fixing item codes and requiring work orders for issues usually does more for availability than any reorder formula.
In HYP, spare parts sit in the same inventory as other stock, with their own stores, min and max levels, and issues linked to maintenance work orders and assets. See how it works on our Maintenance Management page.
Related reading: planned demand starts with the schedule. See Preventive Maintenance Schedules: Planning Service by Date, Running Hours or Meter Reading.