- Not all spares are equal: criticality, failure likelihood, lead time, alternatives and cost all matter.
- ABC analysis ranks by annual consumption value, not by operational criticality. Use both.
- Reorder point = expected demand during lead time + safety stock.
- Inventory position must include outstanding orders and reserved stock, not just what is on the shelf.
- More stock is not automatically better; excess inventory costs money and can become obsolete.
A machine breaks down because of a damaged bearing. The team identifies the problem and prepares the repair, but the bearing is not in the store. The machine stays stopped while the factory looks for a supplier. This is an inventory problem that has become a production problem.
Why spare parts management matters
A standard bolt may come from several suppliers. A specialised pump component may have a long lead time and no substitute. Managing both identically creates either unnecessary cost or exposure to downtime. Effective management helps to:
- Reduce stockouts of critical components.
- Avoid unnecessary purchases.
- Improve repair readiness.
- Control inventory cost.
- Track actual parts consumption.
- Improve purchasing decisions.
- Connect parts usage with equipment history.
What is MRO inventory?
MRO stands for Maintenance, Repair and Operations: the parts, supplies and consumables used to support the operation and maintenance of a facility, not usually sold as part of the finished product.
| Category | Examples |
|---|---|
| Mechanical components | Bearings, belts, seals, couplings |
| Electrical components | Fuses, relays, contactors, cables |
| Lubricants | Grease, hydraulic oil, machine oil |
| Pneumatic components | Valves, fittings, cylinders |
| Maintenance consumables | Filters, cleaning supplies, fasteners |
| Safety-related supplies | Approved maintenance PPE and replacement safety components |
How to identify critical spare parts
- Equipment criticality: a spare for a machine that can stop the whole line deserves higher priority than one for non-critical equipment.
- Failure likelihood: use failure records and expected component life.
- Supplier lead time: a part available locally within hours is a different risk from one that takes weeks.
- Availability of alternatives: do not assume another part is compatible because it looks similar; substitutes must be approved.
- Financial impact: weigh the cost of stocking against the operational cost of not having it. A critical part can justify holding stock even when expensive.
ABC analysis for spare parts
Annual Consumption Value = Annual Quantity Used × Unit Purchase Cost.
| Category | Meaning | Management approach |
|---|---|---|
| A | Higher annual consumption value | More detailed monitoring and control |
| B | Medium annual consumption value | Regular review |
| C | Lower annual consumption value | Simpler controls where appropriate |
Set the percentage boundaries from your own inventory distribution. Note that ABC analysis does not measure operational criticality: a cheap item with tiny annual consumption can still stop an important line. Use it alongside equipment criticality and lead time.
How to calculate a reorder point
Reorder Point = Expected Demand During Lead Time + Safety Stock.
Worked example: a factory uses about four filters a week and the supplier takes three weeks to deliver, so demand during lead time is 4 × 3 = 12 filters. With five filters of safety stock, the reorder point is 12 + 5 = 17. When the inventory position reaches 17, purchasing is triggered.
Inventory position should count outstanding orders and stock reserved for other jobs, not only the physical quantity in the store. This is a simplified calculation; real planning should also account for consumption variability, delivery uncertainty, minimum order quantities and service-level requirements.
How to determine safety stock
Safety stock is extra inventory held against uncertainty, such as deliveries that sometimes take longer than the usual two weeks. Consider demand variation, supplier reliability, lead time, the consequences of a stockout and whether alternative suppliers exist. Higher stock is not automatically better: excess inventory adds storage cost, ties up working capital and can become obsolete.
Seven practical ways to improve spare parts management
One record per part: unique number, description, manufacturer, approved specification, compatible machines, location, supplier and unit cost. This ends multiple names for the same component.
Record which machines use each part, so the impact of a shortage is visible.
Receipts, issues, returns, transfers and adjustments. Without them, system stock drifts away from the physical count.
Review critical components regularly against reorder points, lead times and equipment criticality.
Compatible components can reduce the number of items stocked, but substitutions must be approved by responsible technical staff.
Find parts tied to retired or modified equipment. Holding them adds cost without improving availability.
Machines that consume the most parts may have recurring failures, poor installation practice or deteriorating equipment.
How a CMMS improves spare parts management
A CMMS ties maintenance work to inventory. A technician requests a bearing for a work order, the store keeper reviews it, the part is issued and the movement becomes part of the maintenance record. Firmicore provides an inventory and parts module with a categorised catalogue, stock movement records, multi-stage approval workflows, purchase orders, supplier management and low-stock alerts on applicable plans. See how it fits with work orders and the wider maintenance platform.
Frequently asked questions
How many spare parts should a manufacturing plant keep?
There is no standard quantity. Stock levels depend on equipment criticality, consumption, supplier lead time, stockout consequences and component availability.
What is the difference between MRO and raw-material inventory?
MRO inventory supports equipment maintenance and facility operations. Raw materials are consumed or transformed during production of the finished product.
What is a spare-parts reorder point?
The inventory level at which replenishment should be initiated. It commonly equals expected consumption during supplier lead time plus safety stock.
How can factories reduce excess spare-parts inventory?
Review consumption patterns, remove obsolete items, set realistic reorder points, improve supplier coordination and separate critical components from low-impact stock.
Why is spare-parts tracking important for maintenance teams?
Parts consumption shows maintenance cost, recurring failures, machine reliability and replacement needs.
Final thoughts
Good spare-parts management means the right parts are available when maintenance needs them, without tying up capital in stock that rarely moves. When machine records, work orders and inventory are connected, a factory sees what it consumes and why.
- Understanding Reorder Point Planning — SAP Learning
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Start FreeTharindu (Founder, Lumora Ventures) works with manufacturing teams in Sri Lanka and Southeast Asia to design practical maintenance software for real factory constraints.