Bad spare parts management costs maintenance teams money in two directions simultaneously. Too much inventory ties up capital in parts that sit on shelves for years. Too little inventory causes two-day repair delays when the right part isn't in stock. Most teams suffer both problems at once: expensive critical spares in oversupply while routine consumables run out every month.
The fix is a classification system and minimum stock levels. Here is how to build both.
Step 1: Audit What You Have
Before optimising anything, know what you have. A physical count of your maintenance storeroom — ideally imported into a CMMS — reveals three things that most teams find surprising:
- Obsolete parts — spare parts for assets that were replaced or disposed of years ago
- Unknown stock — parts with no label, no asset association, and no one who knows why they're there
- Duplicates — the same part stored under three different names in three different bins
A one-time storeroom audit, combined with a parts import to your CMMS, typically identifies 10–30% of inventory as dead stock that can be written off.
Step 2: Classify Parts Using ABC Analysis
ABC classification sorts parts by consumption value — the combination of how often you use them and how much they cost.
| Class | Criteria | Strategy | |-------|----------|----------| | A | High consumption × high cost — top 10-20% of parts, 70-80% of total inventory value | Tight control, frequent reorder checks, minimum stock well-defined | | B | Medium consumption or medium cost — next 30% of parts | Moderate control, review quarterly | | C | Low consumption, low cost — bottom 50% of parts | Loose control, reorder when empty |
ABC analysis reverses how most teams manage parts. They spend energy on the cheap consumables (C parts) because there are so many SKUs, while expensive capital items (A parts) go unmonitored.
Step 3: Add a Criticality Layer
ABC analysis tells you about cost and usage. It doesn't tell you about criticality — the consequence of not having the part when you need it.
Combine ABC with a criticality rating:
| Criticality | Definition | |-------------|-----------| | Critical | Production stops, safety risk, or regulatory breach if this part is not available | | Important | Significant delay or degraded operation if unavailable | | Standard | Inconvenient if unavailable, but alternative methods exist |
A part that is "C" on ABC analysis but "Critical" on criticality still needs to be stocked. It's used rarely, but when it fails — nothing works until the part arrives.
Step 4: Set Min/Max Stock Levels
For each part, set:
- Minimum stock (reorder point): The level at which a replenishment order should be placed
- Maximum stock: The level at which the bin is considered full
Calculating the minimum:
Min = (Average daily usage × Lead time in days) + Safety stock
Safety stock is typically 1–2 weeks of average usage for A parts, and 1x usage for B parts.
Example: A hydraulic seal used 2 per week on average, with a supplier lead time of 5 days:
- Average daily usage = 2/7 = 0.28 units/day
- Lead time consumption = 0.28 × 5 = 1.4 units
- Safety stock = 1 week of usage = 2 units
- Minimum = 1.4 + 2 = 3.4 → round up to 4 units
Set the maximum at 2–3 weeks of supply for most parts. Over-stocking creates carrying costs and expiry risk.
Step 5: Link Parts to Assets and Work Orders
The most powerful spare parts management practice is linking:
- Parts → Assets they belong to (so you know what's needed when an asset fails)
- Parts → Work orders (so consumption is tracked automatically as WOs are completed)
With this linkage, your CMMS tracks current stock levels without manual counting. When a PM work order requires a filter change and the technician logs the part, inventory decreases by one. When stock drops below minimum, you get an alert.
Without this linkage, you're counting parts manually and constantly surprised when stock runs out.
Reducing Carrying Costs Without Creating Stockouts
Common mistakes in trying to reduce inventory:
Cutting safety stock too aggressively: Reducing safety stock from 2 weeks to 3 days saves inventory capital but creates high downtime risk. Any supplier delay or demand spike causes a stockout.
Eliminating C parts entirely: Just because a part is rarely used doesn't mean it can be ordered on demand. Lead time matters more than usage frequency for critical C parts.
Not adjusting for seasonality: HVAC filters needed every summer, heating parts needed every winter. Usage patterns matter for accurate minimums.
A better approach: focus first on eliminating confirmed dead stock (no asset association, no recent usage), then review your A-class parts for over-stocking based on actual usage history.
Vendor Lead Times and the Hidden Downtime Risk
Lead time data is essential for setting minimums accurately, but most teams don't track it. Signs of a lead time problem:
- You routinely run out of parts before the reorder arrives
- Emergency expediting fees are a regular budget line item
- Certain repairs always take days longer than expected
Fix: log actual lead times against supplier orders in your CMMS. After 3–6 months, you have real lead time data instead of estimates. Recalculate minimums using actual data.
Maintoro includes parts inventory management linked to work orders and assets. Set minimum/maximum stock levels, track consumption automatically through WO completion, and get alerts when minimums are reached. Free plan includes inventory management.
Related reading
- Spare parts management complete guide — ABC, criticality, min/max formulas
- Spare parts list template — Excel-ready parts register
- CMMS implementation guide — where parts inventory fits in rollout sequence
- CMMS for warehouses — parts-heavy 3PL and DC operations
- Maintoro features — parts inventory linked to work orders