If you build custom machinery, custom equipment, or made-to-order assemblies, managing the parts list is a central project workflow. Unlike high-volume manufacturers who repeat the same builds, assembly companies work with unique configurations, different suppliers, variable lead times, and a customer waiting for a delivery date.
This guide is written specifically for small assembly companies — typically 1–50 employees — who need to manage parts lists for project-based work.
What Makes Assembly Parts List Management Different?
High-volume manufacturers can invest in complex MRP systems that plan production runs weeks or months in advance. Assembly companies don't have that luxury. Your challenges are different:
- Every project is different. You can't rely on standard BOMs — every machine may have a different specification, different options, and different quantities.
- Lead times are critical. When a customer has a Factory Acceptance Test (FAT) date booked, late parts mean late delivery — and potential penalties.
- Stock is shared across projects. Common components may be used across several active projects simultaneously, creating competition for the same stock.
- Suppliers vary by project. Different customers may specify different preferred suppliers, or certain components may only be available from one source.
- Costs need tracking. You've quoted a fixed price to your customer. Every purchasing decision affects your margin.
The Parts List Workflow for Assembly Projects
A well-managed parts list follows the same broad workflow on every project. A clear process gives the team a way to plan deliveries and address exceptions.
Step 1: Create the BOM from Engineering
Your parts list starts with the engineering BOM — typically derived from CAD drawings or a design spreadsheet. The sooner this is complete and accurate, the sooner purchasing can start.
Common delay: Engineering changes after purchasing has started. A good parts list system allows changes to be tracked and communicated, so purchasing can review affected orders.
Step 2: Check Available Stock
Before raising any purchase orders, check what you already have. For assembly companies with ongoing projects, stock levels fluctuate constantly. A centralized stock management system that's linked to the parts list will automatically show you how much of each component is available for this project — taking into account what's already allocated to other jobs.
Step 3: Identify Long Lead Time Items
Not all parts are equal. A standard bolt may have a short lead time while a custom motor may take considerably longer. Identifying long lead time items early helps the team plan procurement.
Best practice: highlight any item with a lead time greater than 4 weeks at the start of every project and escalate immediately if it hasn't been ordered within the first week.
Step 4: Raise Quote Requests
For items without a current price — either new components or components where prices have changed — send quote requests to suppliers before raising purchase orders. This gives you current cost data for project cost tracking.
Step 5: Raise Purchase Orders
Once you have prices, raise purchase orders with accurate part references, quantities, and required delivery dates. Sending a purchase order with the correct supplier reference (not just your internal part number) helps the supplier match the order to the intended component.
Step 6: Track Deliveries Against Required Dates
A single late component can prevent assembly, delay commissioning, and push back the entire test date. Proactive delivery tracking — comparing supplier commit dates against your required dates — identifies which orders need follow-up or alternatives.
Common Parts List Management Mistakes
Starting Procurement Too Late
Waiting for a fully signed-off BOM before placing any orders can put long lead time items at risk. Identify those items early and review any provisional orders against the confirmed BOM before committing further.
Not Tracking Stock Usage Across Projects
If two project managers both allocate the same stock to their respective projects, the allocation needs review. Centralized stock management records allocations against projects so the team can identify conflicts.
Losing Track of Open Orders
Without a centralized purchase order register, it's easy to lose track of what's been ordered, what's been received, and what's still outstanding. This leads to duplicate orders, missed deliveries, and invoice disputes.
Choosing the Right Tool
The right parts list management tool for a small assembly company should have a workflow the whole team can use and connect to stock, purchase orders, and project costs.
AssembleFlow was built by engineers who have managed exactly these challenges in real assembly workshops. It's designed to handle the full parts list workflow — from BOM creation to final delivery — in one place.
Start your free 14-day trial and see how it works for your next project.
Frequently Asked Questions
What is the difference between a parts list and a BOM?
In most machine-building shops the terms are used interchangeably. A parts list is the working list of components for a build; a BOM is the same list with the structure and data needed for purchasing and production.
How do I manage parts lists for one-off machines?
Start each build from a clean assembly-grouped list, keep drawing issues current, check stock before ordering, and track every part from inquiry to goods received in one place.
Free tools: the Excel templates (BOM, PO tracker, cost and quote worksheet), the margin calculator and a product tour need no sign-up.