Flat-bed machines typically attach to the table or a special A- or tilt-stand with special clamps. The metal bed makes the machines somewhat heavy but also very durable. Metal flatbeds are also more prone to rust than plastic flatbed machines.
Metal flatbed machines come in fine, mid-, standard, and bulky gauges.
Metal flatbed machines are still manufactured in limited quantities. Vintage metal flatbed machines were manufactured by Japanese companies Singer/Studio/Silver Reed, Brother and Toyota. Most of the machines below I had personal experience with.
BROTHER knitting machines
Brother KH210, bulky, manual
Brother KH220, bulky, manual
Brother KH230, bulky, manual
Brother KH260, bulky, punchcards
Brother KH270, bulky, electronic
Brother KH35, standard, manual
Brother Profile 500, standard, manual
Brother KH521, standard, 4-push-button
Brother KH531, standard, 4-push-button
Brother Profile 551, standard, 4-push button
Brother Profile 552, standard, 8-push button
Brother KH560, standard, 8-push button
Brother KH561, standard, 8-push button
Brother KH571, standard, 8-push button
Brother KH581, standard, 8-push button
Brother KH583, standard, 8-push button
Brother Profile/KH585, standard, 8-push button
Brother KH587, standard, 8-push button
Brother Profile/KH588, standard, 8-push button
Brother KH601, standard, 8-push button
Genie (Brother) KH710, standard, 8-push button
Brother KH800, standard, punchcards
Brother KH801, standard, punchcards
Brother KH810, standard, punchcards
Brother KH811, standard, punchcards, also pushbuttons
Brother KH821, standard, punchcards
Brother KH830, standard, punchcards
Brother KH831, standard, punchcards
Brother KH836, standard, punchcards
Brother KH838, standard, punchcards
Brother KH840, standard, punchcards
Brother KH851, standard, punchcards
Brother KH860, standard, punchcards
Brother KH864, standard, punchcards
Brother KH868, standard, punchcards
Brother (Palie) KH871, standard, punchcards
Brother KH880, standard, punchcards
Brother KH881, standard, punchcards
Brother KH890, standard, punchcards
Brother KH891, standard, punchcards
Brother KH892, standard, punchcards
Brother KH893, standard, punchcards
Brother KH894, standard, punchcards
Brother KH900, standard, electronic
Brother KH910, standard, electronic, mylar sheets
Brother KH930, standard, electronic
Brother KH940, standard, electronic
Brother KH950, standard, electronic
Brother KH950e, standard, electronic
Brother KH950i, standard, electronic
Brother KH965, standard, electronic
Brother KH965i, standard, electronic
Brother KH970, standard, electronic
SINGER knitting machines
Singer MemoMatic 210, standard, punchcards
Singer MemoMatic 321, standard, punchcards
Singer MemoMatic 328, standard, punchcards
Singer MemoMatic 360K, standard, punchcards
Singer MemoMatic 700K, standard, punchcards
STUDIO knitting machines
Studio 305, standard, basic/manual
Studio 310, standard, needle selector
Studio 312, standard, punchcards
Studio 313, standard, punchcards
Studio 315, standard, punchcards
Studio 321, standard, punchcards
Studio 321, standard, punchcards
Studio mod.326, standard, punchcards
Studio mod.360K, standard, punchcards