Step 5: Choosing a holder
Quickchange toolposts have standard sizes, 100 series (AXA), 200 series (BXA), 300 series (CXA), etc. If you just got your lathe, the toolpost should say which series it is. Techshop lathes use a 250-222 toolpost, which is a 200 series/BXA toolpost. All 200 series toolholders will fit the 200 series toolpost, and similarly, for 300 series holders and posts. However, a 200 series toolholder would not fit on a 300 series toolpost.
The toolholders themselves are also standardized. Different varieties typically come in all common toolpost sizes. Again, most tool supplies should have a wide selection, KBC, MSC, SHARS, etc. For most turning and facing tools, a #1 or #2 toolholder will be the best choice. For boring bars, a #2 or #4 holder will be best. Keep in mind, the toolholders have a maximum tool size, for 200 Series/BXA toolholders #1 and #2, a 5/8ths tool will be the largest you can hold. You have to choose smaller tools based on your toolpost.
Here, I chose a single BXA #2 toolholder. This holder accepts the SCLC tool, and has a v-groove for the S-SCLC boring bar, meaning only one holder is necessary.