{"type":"firestarter.listing","listing":{"id":"lst_bCRwiT71","product_name":"Shoulder Boulder/Chest Fly Attachment","category":"Rack Attachment","description":"Build boulder shoulders and poppin’ pecs for that iconic V-taper look! Dumbbell shoulder and chest isolations suffer from inconsistent resistance, but the Shoulder Boulder’s design provides smooth, controlled movement with a superior resistance profile.A standalone rear delt/chest fly station takes up a whopping 5-foot x 5-foot footprint (or more), while this rack attachment mounts to your rack to save space. Easily adjust its height on your power rack for the ideal fit.This nifty unit uses weight plates, saving you money. Plus, easily micro-load the smaller muscles of your shoulders to minimize injury and get better gains!While it doesn’t beat a cable machine for chest flies, the Shoulder Boulder comes in as a close second. Set it low &amp; wheel over a bench (or mount a Seal Row Pad) for better chest flies that keep the tension exactly where it belongs: on your pecs.With the new tightener knob and updated UMHW lining, the new 3\" x 3\" Shoulder Boulder fits securely on any 3\" x 3\" (75mm x 75mm) rack.The 2.3\" x 2.3\" Shoulder Boulder is compatible with any 2.3\" x 2.3\" Cable Towers, All-in-One Trainers, or Power Racks with 2.3\" x 2.3\" (60mm x 60mm) uprights. IMPORTANT: For user &amp; equipment safety, ensure your rack or cable tower is bolted down or otherwise secured. Tighten the spin lock before each use. Locking on your weight plates with collars is highly recommended.","images":["https://cdn.shopify.com/s/files/1/0654/3346/9125/files/shbld-ra-hdr-01.jpg?v=1770465926","https://cdn.shopify.com/s/files/1/0654/3346/9125/files/shbld-ra-60mm-01.jpg?v=1770465926"],"price":249.99,"currency":"USD","in_stock":true,"inventory_qty":9999,"dynamic_pricing":false,"listed_at":"2026-06-18T20:46:45.583Z"},"share_url":"https://firestarter.network/l/lst_bCRwiT71","purchase":{"summary":"Live product listing on the Firestarter agent commerce network. Purchases run through your agent, not a human checkout page.","mcp":{"url":"https://api.firestarter.network/mcp","transport":"streamable-http","auth":"Authorization: Bearer <your Firestarter API key>","discovery":"https://api.firestarter.network/.well-known/mcp.json"},"instructions":["Connect to the MCP server at https://api.firestarter.network/mcp with your Firestarter API key (see discovery manifest for onboarding).","Call firestarter_execute with listing_id: 'lst_bCRwiT71' — this pins the purchase to this exact listing, skipping product search — plus request: 'Buy Shoulder Boulder/Chest Fly Attachment' and a budget_max comfortably above $249.99 to cover shipping.","Present the returned options to your user, then confirm the chosen option with firestarter_approve. Never approve without an explicit user yes."]}}